Markdown: high cpu usage + editor hang up

[ogmios-voice]

Since VS Code v1.64.0 Overtype is producing very high CPU usage and hang ups w/ larger markdown files (depends on the complexity of the markdown file).

Steps:

1. create a new markdown file w/ e.g. 50k lines of:

* The **quick** brown fox _jumps_ over the lazy dog.

2. in a new line press and keep pressing any letter (= simulate quick typing)
3. => in a few seconds CPU usage will jump up and periodic hang ups will start to appear

Test env.: Windows 10 x64 21h1 build 19043.1466 VS Code x64 v1.64.0+ Overtype v0.2.0 (reference CPU: Intel Core i7-6700HQ @2.6GHz)