feat: Publish platform-specific Code VSIXes

[lnicola]

Closes #10483
CC #10371

Some notes:

• we still build a plain VSIX, just in case
• we build the extension on every platform to make the release workflow arguably cleaner
• the Windows VSIX includes the PDB (but let's leave Backtraces on windows #10371 open until we change the Windows stand-alone release to a ZIP file)
• npm doesn't run if started from xtask, possibly something related to path mapping; I moved the npm calls outside, but..
• the Patch thingy doesn't work any more, so you'll end up with a dirty package.json of you run cargo xtask --client-patch-version; I don't think we should block on this
• there's an untested Alpine build; for better or worse, we publish musl builds as alpine
• I tested this as much as I could, but not the publishing and nightly updates
• you can find some sample artifacts under https://github.com/lnicola/rust-analyzer/releases
• we can now run the server from the install location (is Code planning to switch to compressed extensions?), except on NixOS
• Code lets you install a VSIX for the wrong platform (with the results one would expect)
• I don't know what happens if we try to publish a VSIX without a target

This is a relatively risky, but we'll probably have to take our chances with it.

r? @rust-analyzer/review

[matklad]

will this do the right thing? I am thinking about --packagePath foo bar vs --packagePath foo --packagePath bar.

[lnicola]

I hope so, the help says:

  -i, --packagePath <paths...>    Publish the provided VSIX packages.

[matklad]

bors r=me

Seems broadly reasonable! Let's see if the nightly works!

[matklad]

(seeing most of ra team online at this late hour warms my heart :-)

[SomeoneToIgnore]

This is a relatively risky

I wonder, would doing that after Monday's release be safer?

[lnicola]

I wonder, would doing that after Monday's release be safer?

We still have to do it before a Monday, unless we make a special holidays release tomorrow (which I wouldn't mind). It's quite hard to test otherwise.

[matklad]

Not sure -- there's a stretch of holidays ahead, so it might makes sense to pack as much breakage as possible before that.

[bors]

Build succeeded:

• Rust (macos-latest)
• Rust (ubuntu-latest)
• Rust (windows-latest)
• TypeScript (ubuntu-latest)
• TypeScript (windows-latest)

[matklad]

I like the idea of bonus christmas release :)

[lnicola]

Or rather a "I'll probably have other non-holiday stuff on Monday, and I'd rather fix any fallout tomorrow instead" release.

[lnicola]

By the way, thanks for the quick reviews!