patch 8.2.1015: popup filter gets key with modifier prepended

Problem:    Popup filter gets key with modifier prepended when using
            modifyOtherKeys.
Solution:   Remove the shift modifier when it is included in the key, also
            when the Alt or Meta modifier is used.
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index 2188c2c..b6f718c 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -2079,9 +2079,9 @@
   " check size with wrapping lines
   call term_sendkeys(buf, "j")
   call VerifyScreenDump(buf, 'Test_popupwin_scroll_12', {})
-  call term_sendkeys(buf, "x")
 
   " clean up
+  call term_sendkeys(buf, "x")
   call StopVimInTerminal(buf)
   call delete('XtestPopupScroll')
 endfunc
@@ -3347,6 +3347,12 @@
   call feedkeys("\u301b", 'xt')
   call assert_equal([0xe3, 0x80, 0x9b], g:bytes)
 
+  if has('unix')
+    " with modifyOtherKeys <M-S-a> does not include a modifier sequence
+    call feedkeys("\<Esc>[27;4;65~", 'Lx!')
+    call assert_equal([0xc3, 0x81], g:bytes)
+  endif
+
   call popup_clear()
   delfunc MyPopupFilter
   unlet g:bytes