patch 8.2.1498: on slow systems tests can be flaky

Problem:    On slow systems tests can be flaky.
Solution:   Use TermWait() instead of term-wait(). (Yegappan Lakshmanan,
            closes #6756)
diff --git a/src/testdir/test_terminal3.vim b/src/testdir/test_terminal3.vim
index 30ff3e7..e982190 100644
--- a/src/testdir/test_terminal3.vim
+++ b/src/testdir/test_terminal3.vim
@@ -374,7 +374,7 @@
   call term_sendkeys(buf, ":set mouse=a term=xterm ttymouse=sgr\<CR>")
   call term_sendkeys(buf, ":set clipboard=\<CR>")
   call term_sendkeys(buf, ":set mousemodel=extend\<CR>")
-  call term_wait(buf)
+  call TermWait(buf)
   redraw!
 
   " Use the mouse to enter the terminal window
@@ -388,9 +388,9 @@
   call feedkeys("\<LeftMouse>\<LeftRelease>", 'xt')
   call test_setmouse(3, 8)
   call term_sendkeys(buf, "\<LeftMouse>\<LeftRelease>")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call term_sendkeys(buf, ":call writefile([json_encode(getpos('.'))], 'Xbuf')\<CR>")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   let pos = json_decode(readfile('Xbuf')[0])
   call assert_equal([3, 8], pos[1:2])
 
@@ -400,9 +400,9 @@
   call term_sendkeys(buf, "\<LeftMouse>")
   call test_setmouse(2, 16)
   call term_sendkeys(buf, "\<LeftRelease>y")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call term_sendkeys(buf, ":call writefile([@\"], 'Xbuf')\<CR>")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call assert_equal('yellow', readfile('Xbuf')[0])
 
   " Test for selecting text using doubleclick
@@ -411,18 +411,18 @@
   call term_sendkeys(buf, "\<LeftMouse>\<LeftRelease>\<LeftMouse>")
   call test_setmouse(1, 17)
   call term_sendkeys(buf, "\<LeftRelease>y")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call term_sendkeys(buf, ":call writefile([@\"], 'Xbuf')\<CR>")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call assert_equal('three four', readfile('Xbuf')[0])
 
   " Test for selecting a line using triple click
   call delete('Xbuf')
   call test_setmouse(3, 2)
   call term_sendkeys(buf, "\<LeftMouse>\<LeftRelease>\<LeftMouse>\<LeftRelease>\<LeftMouse>\<LeftRelease>y")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call term_sendkeys(buf, ":call writefile([@\"], 'Xbuf')\<CR>")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call assert_equal("vim emacs sublime nano\n", readfile('Xbuf')[0])
 
   " Test for selecting a block using qudraple click
@@ -431,9 +431,9 @@
   call term_sendkeys(buf, "\<LeftMouse>\<LeftRelease>\<LeftMouse>\<LeftRelease>\<LeftMouse>\<LeftRelease>\<LeftMouse>")
   call test_setmouse(3, 13)
   call term_sendkeys(buf, "\<LeftRelease>y")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call term_sendkeys(buf, ":call writefile([@\"], 'Xbuf')\<CR>")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call assert_equal("ree\nyel\nsub", readfile('Xbuf')[0])
 
   " Test for extending a selection using right click
@@ -442,9 +442,9 @@
   call term_sendkeys(buf, "\<LeftMouse>\<LeftRelease>")
   call test_setmouse(2, 16)
   call term_sendkeys(buf, "\<RightMouse>\<RightRelease>y")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call term_sendkeys(buf, ":call writefile([@\"], 'Xbuf')\<CR>")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call assert_equal("n yellow", readfile('Xbuf')[0])
 
   " Test for pasting text using middle click
@@ -452,13 +452,13 @@
   call term_sendkeys(buf, ":let @r='bright '\<CR>")
   call test_setmouse(2, 22)
   call term_sendkeys(buf, "\"r\<MiddleMouse>\<MiddleRelease>")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call term_sendkeys(buf, ":call writefile([getline(2)], 'Xbuf')\<CR>")
-  call term_wait(buf, 50)
+  call TermWait(buf, 50)
   call assert_equal("red bright blue", readfile('Xbuf')[0][-15:])
 
   " cleanup
-  call term_wait(buf)
+  call TermWait(buf)
   call StopVimInTerminal(buf)
   let &mouse = save_mouse
   let &term = save_term
@@ -494,14 +494,14 @@
   let buf = RunVimInTerminal('Xtest_modeless -n', {})
   call term_sendkeys(buf, ":set nocompatible\<CR>")
   call term_sendkeys(buf, ":set mouse=\<CR>")
-  call term_wait(buf)
+  call TermWait(buf)
   redraw!
 
   " Use the mouse to enter the terminal window
   call win_gotoid(prev_win)
   call feedkeys(MouseLeftClickCode(1, 1), 'x')
   call feedkeys(MouseLeftReleaseCode(1, 1), 'x')
-  call term_wait(buf)
+  call TermWait(buf)
   call assert_equal(1, getwininfo(win_getid())[0].terminal)
 
   " Test for copying a modeless selection to clipboard
@@ -514,7 +514,7 @@
   call assert_equal("d green y", @*)
 
   " cleanup
-  call term_wait(buf)
+  call TermWait(buf)
   call StopVimInTerminal(buf)
   let &mouse = save_mouse
   let &term = save_term