Undo on text editor of a webview (custom text editor) rolls back the whole stack

Describe the bug
I have a CustomTextEditor in my extension, with "priority: "option"". Whenever the webview edits the text file, the consequent edits will be undone by 1 'u' key press. ctrl-z works right.

To Reproduce
Steps to reproduce the behavior:

1. Clone vscode-extension-samples
2. Go to the ...\vscode-extension-samples\custom-editor-sample\
3. Change the catScratch custom editor to be priority option>

diff --git a/custom-editor-sample/package.json b/custom-editor-sample/package.json
index 38801cc..1813089 100644
--- a/custom-editor-sample/package.json
+++ b/custom-editor-sample/package.json
@@ -29,7 +29,8 @@
 					{
 						"filenamePattern": "*.cscratch"
 					}
-				]
+				],
+				"priority": "option"
 			},
 			{
 				"viewType": "catCustoms.pawDraw",

4. Start the extension.
5. Open example.cscratch
6. Split right
7. On the right side "Reopen Editor With..." -> Cat Scratch
8. Add 2 "scratch" with the "Scratch!" button
9. Select the text editor
10. Press 'u'

Expected behavior
The editor undoes 1 scratch added. Just like pressing ctrl-z.

Screenshots
https://i.imgur.com/qD1yY8G.gif

Environment (please complete the following information):

• Extension (VsCodeVim) version: v1.18.9
• VSCode version: VSCodium 1.53.2 (system setup)
• OS: Windows_NT x64 10.0.18363

Additional context

    "vim.otherModesKeyBindings": [
        {
            "before": [
                "u"
            ],
            "after": [],
            "commands": [
                {
                    "command": "undo"
                }
            ]
        },
        {
            "before": [
                "<C-r>"
            ],
            "after": [],
            "commands": [
                {
                    "command": "redo"
                }
            ]
        }
    ]

In user settings.json did not help. It might be considered a reliable reproduction of the issue #2007 .

Reproduce the behavior with custom-editor-sample/package.json, the Cat Scratch custom editor, and the vim.otherModesKeyBindings configuration shown in the issue. Start by tracing how the configured undo command is handled for a webview-backed text editor and compare it with Ctrl-Z. Done means one press of “u” undoes only the most recent scratch edit, matching Ctrl-Z.