Avoid blocking main thread when a folder is opened

[karrtikr]

Does this issue occur when all extensions are disabled?: Yes

Version: 1.85.0-insider (user setup)
OS: Windows_NT x64 10.0.22518

These things block main thread significantly when starting up, following observations correspond to this CPU profile, but can be reproduced almost consistently:

• Git extension uses spawn to "get the repository root" which can block over 3 seconds:

Note spawn in NodeJS is known to be synchronous and blocking: microsoft/vscode-python#22146 (comment). We can use worker threads here to spawn in a different thread, we've been doing the same in Python extension when spawning other binaries: microsoft/vscode-python#22146

• WSL recommender extension "gets telemetry" using "readFileSync" in the process, probably not necessary.

• This is probably required but extension host seems to use readFileSync which blocks some time:

[lszomoru]

The Git extension uses spawn for every git operation. If there is a better way of doing things (ex: use workers) then we should explore doing that as it would have significant impact. I will look into this in December.

[aeschli]

I removed the WSL recommender extension: We no longer use it: #198502