patch 8.1.1787: cannot resize a popup window

Problem:    Cannot resize a popup window.
Solution:   Allow for resizing by dragging the lower right corncer.
diff --git a/src/testdir/dumps/Test_popupwin_drag_01.dump b/src/testdir/dumps/Test_popupwin_drag_01.dump
index c8867e3..64afe82 100644
--- a/src/testdir/dumps/Test_popupwin_drag_01.dump
+++ b/src/testdir/dumps/Test_popupwin_drag_01.dump
@@ -7,4 +7,4 @@
 |7| @31|║+0#0000001#ffd7ff255|1@3| @1|║| +0#0000000#ffffff0@33
 |8| @31|║+0#0000001#ffd7ff255|2@5|║| +0#0000000#ffffff0@33
 |9| @31|║+0#0000001#ffd7ff255|3@4| |║| +0#0000000#ffffff0@33
-@33|╚+0#0000001#ffd7ff255|═@5|╝| +0#0000000#ffffff0@15|1|,|1| @10|T|o|p| 
+@33|╚+0#0000001#ffd7ff255|═@5|⇲| +0#0000000#ffffff0@15|1|,|1| @10|T|o|p| 
diff --git a/src/testdir/dumps/Test_popupwin_drag_02.dump b/src/testdir/dumps/Test_popupwin_drag_02.dump
index f03ecb8..2597e1d 100644
--- a/src/testdir/dumps/Test_popupwin_drag_02.dump
+++ b/src/testdir/dumps/Test_popupwin_drag_02.dump
@@ -3,7 +3,7 @@
 |3| @31|║+0#0000001#ffd7ff255|1@3| @1|║| +0#0000000#ffffff0@33
 |4| @31|║+0#0000001#ffd7ff255|2@5|║| +0#0000000#ffffff0@33
 |5| @31|║+0#0000001#ffd7ff255|3@4| |║| +0#0000000#ffffff0@33
-|6| @31|╚+0#0000001#ffd7ff255|═@5|╝| +0#0000000#ffffff0@33
+|6| @31|╚+0#0000001#ffd7ff255|═@5|⇲| +0#0000000#ffffff0@33
 |7| @73
 |8| @73
 |9| @73
diff --git a/src/testdir/dumps/Test_popupwin_drag_03.dump b/src/testdir/dumps/Test_popupwin_drag_03.dump
new file mode 100644
index 0000000..b6b363a
--- /dev/null
+++ b/src/testdir/dumps/Test_popupwin_drag_03.dump
@@ -0,0 +1,10 @@
+>1+0&#ffffff0| @73
+|2| @31|╔+0#0000001#ffd7ff255|═@9|╗| +0#0000000#ffffff0@29
+|3| @31|║+0#0000001#ffd7ff255|1@3| @5|║| +0#0000000#ffffff0@29
+|4| @31|║+0#0000001#ffd7ff255|2@5| @3|║| +0#0000000#ffffff0@29
+|5| @31|║+0#0000001#ffd7ff255|3@4| @4|║| +0#0000000#ffffff0@29
+|6| @31|║+0#0000001#ffd7ff255| +0#4040ff13&@9|║+0#0000001&| +0#0000000#ffffff0@29
+|7| @31|╚+0#0000001#ffd7ff255|═@9|⇲| +0#0000000#ffffff0@29
+|8| @73
+|9| @73
+|:|c|a|l@1| |R|e|s|i|z|e|(|)| @42|1|,|1| @10|T|o|p| 
diff --git a/src/testdir/dumps/Test_popupwin_previewpopup_1.dump b/src/testdir/dumps/Test_popupwin_previewpopup_1.dump
index 06ac4cb..1b87292 100644
--- a/src/testdir/dumps/Test_popupwin_previewpopup_1.dump
+++ b/src/testdir/dumps/Test_popupwin_previewpopup_1.dump
@@ -4,7 +4,7 @@
 |f|o|u|r| |║+0#0000001#ffd7ff255|t|h|e|w|o|r|d| |i|s| |h|e|r|e| @24| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@26
 |f|i|v|e| |║+0#0000001#ffd7ff255|2@1| @37| +0#0000000#0000001|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@26
 |s|i|x| @1|║+0#0000001#ffd7ff255|2|3| @37| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@26
-|s|e|v|e|n|╚+0#0000001#ffd7ff255|═@40|╝| +0#0000000#ffffff0@26
+|s|e|v|e|n|╚+0#0000001#ffd7ff255|═@40|⇲| +0#0000000#ffffff0@26
 |f|i|n|d| >t|h|e|w|o|r|d| |s|o|m|e|w|h|e|r|e| @52
 |n|i|n|e| @70
 |t|h|i|s| |i|s| |a|n|o|t|h|e|r| |w|o|r|d| @54
diff --git a/src/testdir/dumps/Test_popupwin_previewpopup_2.dump b/src/testdir/dumps/Test_popupwin_previewpopup_2.dump
index aa53bb3..131eabe 100644
--- a/src/testdir/dumps/Test_popupwin_previewpopup_2.dump
+++ b/src/testdir/dumps/Test_popupwin_previewpopup_2.dump
@@ -6,7 +6,7 @@
 |s|i|x| @4|║+0#0000001#ffd7ff255|t|h|i|s| |i|s| |a|n|o|t|h|e|r| |p|l|a|c|e| @18| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@23
 |s|e|v|e|n| @2|║+0#0000001#ffd7ff255|2|9| @37| +0#0000000#0000001|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@23
 |f|i|n|d| |t|h|e|║+0#0000001#ffd7ff255|3|0| @37| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@23
-|n|i|n|e| @3|╚+0#0000001#ffd7ff255|═@40|╝| +0#0000000#ffffff0@23
+|n|i|n|e| @3|╚+0#0000001#ffd7ff255|═@40|⇲| +0#0000000#ffffff0@23
 |t|h|i|s| |i|s| >a|n|o|t|h|e|r| |w|o|r|d| @54
 |v|e|r|y| |l|o|n|g| |l|i|n|e| |w|h|e|r|e| |t|h|e| |w|o|r|d| |i|s| |a|l|s|o| |a|n|o|t|h|e|r| @29
 |~+0#4040ff13&| @73
diff --git a/src/testdir/dumps/Test_popupwin_previewpopup_3.dump b/src/testdir/dumps/Test_popupwin_previewpopup_3.dump
index c4ae417..46a3a61 100644
--- a/src/testdir/dumps/Test_popupwin_previewpopup_3.dump
+++ b/src/testdir/dumps/Test_popupwin_previewpopup_3.dump
@@ -6,7 +6,7 @@
 |s|i|x| @10|║+0#0000001#ffd7ff255|t|h|i|s| |i|s| |a|n|o|t|h|e|r| |p|l|a|c|e| @18| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@17
 |s|e|v|e|n| @8|║+0#0000001#ffd7ff255|2|9| @37| +0#0000000#0000001|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@17
 |f|i|n|d| |t|h|e|w|o|r|d| |s|║+0#0000001#ffd7ff255|3|0| @37| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@17
-|n|i|n|e| @9|╚+0#0000001#ffd7ff255|═@40|╝| +0#0000000#ffffff0@17
+|n|i|n|e| @9|╚+0#0000001#ffd7ff255|═@40|⇲| +0#0000000#ffffff0@17
 |t|h|i|s| |i|s| >a|n|o|t|h|e|r| |w|o|r|d| @54
 |v|e|r|y| |l|o|n|g| |l|i|n|e| |w|h|e|r|e| |t|h|e| |w|o|r|d| |i|s| |a|l|s|o| |a|n|o|t|h|e|r| @29
 |~+0#4040ff13&| @73
diff --git a/src/testdir/dumps/Test_popupwin_previewpopup_4.dump b/src/testdir/dumps/Test_popupwin_previewpopup_4.dump
index fc63507..de67fa3 100644
--- a/src/testdir/dumps/Test_popupwin_previewpopup_4.dump
+++ b/src/testdir/dumps/Test_popupwin_previewpopup_4.dump
@@ -7,7 +7,7 @@
 |s+0#0000000#ffffff0|e|v|e|n| @26|║+0#0000001#ffd7ff255|t|h|i|s| |i|s| |a|n|o|t|h|e|r| |p|l|a|c|e| @18| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255
 |f+0#0000000#ffffff0|i|n|d| |t|h|e|w|o|r|d| |s|o|m|e|w|h|e|r|e| @9|║+0#0000001#ffd7ff255|2|9| @37| +0#0000000#0000001|║+0#0000001#ffd7ff255
 |n+0#0000000#ffffff0|i|n|e| @27|║+0#0000001#ffd7ff255|3|0| @37| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255
-|t+0#0000000#ffffff0|h|i|s| |i|s| |a|n|o|t|h|e|r| |w|o|r|d| @11|╚+0#0000001#ffd7ff255|═@40|╝
+|t+0#0000000#ffffff0|h|i|s| |i|s| |a|n|o|t|h|e|r| |w|o|r|d| @11|╚+0#0000001#ffd7ff255|═@40|⇲
 |v+0#0000000#ffffff0|e|r|y| |l|o|n|g| |l|i|n|e| |w|h|e|r|e| |t|h|e| |w|o|r|d| |i|s| |a|l|s|o| >a|n|o|t|h|e|r| @29
 |~+0#4040ff13&| @73
 |~| @73
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index 6033be6..d4b98ae 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -354,6 +354,7 @@
 	call setline(1, range(1, 20))
 	let winid = popup_create(['1111', '222222', '33333'], #{
 	      \ drag: 1,
+	      \ resize: 1,
 	      \ border: [],
 	      \ line: &lines - 4,
 	      \ })
@@ -362,6 +363,11 @@
 	endfunc
 	map <silent> <F3> :call test_setmouse(&lines - 4, &columns / 2)<CR>
 	map <silent> <F4> :call test_setmouse(&lines - 8, &columns / 2)<CR>
+	func Resize()
+	  call feedkeys("\<F5>\<LeftMouse>\<F6>\<LeftDrag>\<LeftRelease>", "xt")
+	endfunc
+	map <silent> <F5> :call test_setmouse(6, 41)<CR>
+	map <silent> <F6> :call test_setmouse(7, 45)<CR>
   END
   call writefile(lines, 'XtestPopupDrag')
   let buf = RunVimInTerminal('-S XtestPopupDrag', #{rows: 10})
@@ -370,6 +376,9 @@
   call term_sendkeys(buf, ":call Dragit()\<CR>")
   call VerifyScreenDump(buf, 'Test_popupwin_drag_02', {})
 
+  call term_sendkeys(buf, ":call Resize()\<CR>")
+  call VerifyScreenDump(buf, 'Test_popupwin_drag_03', {})
+
   " clean up
   call StopVimInTerminal(buf)
   call delete('XtestPopupDrag')