undo/redo search and replace operations is non-atomic and slow

Describe the bug

undo/redo a "search and replace" operation is non-atomic and thus very slow.

First I had the issue with the search and replace being non-atomic. But I found this issue which suggested activating neovim, and it worked:

https://github.com/VSCodeVim/Vim/issues/737

However, it did not make the undo/redo atomic.

To Reproduce

1. Open a non-trivial file (200 rows and 30 replaces takes almost 2 full seconds on my laptop)
2. Type :
3. Type %s/something/blahblahblah/g and hit enter
4. Type u

I can see how the undo operation slowly rewrites the document. If I press ctrl+r to redo the operation it is also slow and non-atomic.

Expected behavior
An atomic and quick undo/redo.

Environment (please complete the following information):

• Extension (VsCodeVim) version: 1.11.3
• VSCode version: 1.40.1
• OS: Windows 10

Start by reproducing the search-and-replace sequence on a non-trivial file: enter :%s/something/blahblahblah/g, then undo with u and redo with ctrl+r. Trace the command and undo/redo handling from that entry point; done means both operations are quick and atomic rather than visibly rewriting the document.