patch 9.0.0439: cursor wrong if inserting before line with virtual text above

Problem:    Cursor wrong if inserting before line with virtual text above.
Solution:   Add the width of the "above" virtual text to the cursor position.
            (issue #11084)
diff --git a/src/testdir/test_textprop.vim b/src/testdir/test_textprop.vim
index d89f84c..f97772c 100644
--- a/src/testdir/test_textprop.vim
+++ b/src/testdir/test_textprop.vim
@@ -2865,6 +2865,11 @@
   let buf = RunVimInTerminal('-S XscriptPropsWithTextAbove', #{rows: 9, cols: 60})
   call VerifyScreenDump(buf, 'Test_prop_with_text_above_1', {})
 
+  call term_sendkeys(buf, "ggI")
+  call VerifyScreenDump(buf, 'Test_prop_with_text_above_2', {})
+  call term_sendkeys(buf, "inserted \<Esc>")
+  call VerifyScreenDump(buf, 'Test_prop_with_text_above_3', {})
+
   call StopVimInTerminal(buf)
 endfunc