Undo incorrectly applies autocompletion

[macp3o]

Issue Type: Bug

Suggested solution: Disable autocompletion during undo.

Steps to reproduce the problem:

1. Enter the following code in an html file: <script>text</script>
2. Delete the closing > of the <script> tag. yielding <scripttext</script>
3. Press Ctl+Z to undo. Undo should restore the deleted > only and show the original code from step 1. However, we get <script></script>text</script> (notice the extra </script>).

VS Code version: Code 1.28.1 (3368db6, 2018-10-11T18:07:34.132Z)
OS version: Linux ia32 4.4.0-137-generic

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• Undoing several newlines should undo them all together (or whichever was added at the same time) (#46152)
• Undo (Ctrl+Z) when doing search-replace from the search window GUI does not work (#20026)
• Autoindent inserts extra undo item, requires double undo after paste (#30406)
• Create undo stops also based on time between edits (#34073)

[aeschli]

duplicate of #34484