Automatically download and update PowerShell Editor Services for LSP

[oWretch]

Download Editor Services and cache, checking for updates as required.

To get v0.2.0 to compile, I had to comment out some keywords in highlights.scm as they prevented the compiled extension from loading

• clean
• define
• from
• using
• var

I tried updating to the latest grammar version, but this didn't help.

Closes #2
Closes #6
Closes #8

[oWretch]

Formatting is working. Need to validate more on suggestions. Suggestions are working too

[JadenMajid]

Closes #8

[notpeter]

I gave this a whirl on macOS, it managed to install/start PowerShell Editor Services properly. Nice!

I also took a stab at some basic docs which we can publish once this is broadly available. Let me know if I can be of assistance getting this merged and an updated version published in the Zed Extension store.

[notpeter]

Bump @wingyplus
Would you like some help maintaining this extension? (I work at Zed)

[wingyplus]

It is fine to comment this out on this PR. Let's fix the highlights.scm to make it work again on another PR.

[wingyplus]

@oWretch @notpeter Sorry for the silence for a long time. I have been really busy this year. :(

This PR LGTM to me. So I'm going to merge it. But before we release a new version, I need someone to fix & sync highlights.scm from upstream to make it work again. Anyone interested in tackling this issue?