Modify the tsconfig.json in lib/vscode/src/build.

This adds the flag skipLibCheck: true to tell TypeScript
to not type-check the declaration files at build time.

We need to add this because otherwise it checks the declaration
files and reports an error of duplicate type definitions
because we use Jest for our tests and they use Mocha and they
both use the global namespace "test" in their .d.ts files.

See also https://github.com/cdr/code-server/pull/2529#issuecomment-763829674

pathProxy.ts: Implement --proxy-path-passthrough

This had me very confused for quite a while until I did a binary search
inspection on route/index.ts. Only with the heart.beat line commented
out did my tests pass without leaking.

They weren't leaking fds but just this heartbeat timer and node of
course prints just fds that are active when it detects some sort of leak
I guess and that made the whole thing very confusing. These fds are not
leaked and will close when node's event loop detects there are no more
callbacks to run.

no of handles 3

tcp stream {
  fd: 20,
  readable: false,
  writable: true,
  address: {},
  serverAddr: null
}

tcp stream {
  fd: 22,
  readable: false,
  writable: true,
  address: {},
  serverAddr: null
}

tcp stream {
  fd: 23,
  readable: true,
  writable: false,
  address: {},
  serverAddr: null
}

It kept printing the above text again and again for 60s and then the
test binary times out I think. I'm not sure if it was node printing the
stuff above or if it was a mocha thing. But it was really confusing...

cc @code-asher for thoughts on what was going on.

edit: It was the leaked-handles import in socket.test.ts!!!
Not sure if we should keep it, this was really confusing and misleading.

cc @code-asher

The goal is to remove supertest as it does not support typescript well
and there's really no good reason for the dependency. Also no websocket
testing support.

express requires all 4 arguments to be declared for a error handler.
It's very unfortunate that our types do not handle this.

And the concerns surrounding it.

Closes #2485

Closes #2222

vscode.ts: Fix close current folder

Fixes VscodeProvider to correctly obey the ew parameter.

Based on changes by @rdbeach. See the previous commit.

When you choose to close the current folder, it doesn't close properly
because the lastVisiited setting is still use. This fixes that.

feat(extensions): add helper header above extensions search

Add a short message above the search box on the Extensions panel. This
helps explain the extension divergence to the user.

If they click dismiss, it stores an item in localStorage to prevent the
message from showing up on subsequent loads.
Co-authored-by: NAsher <ash@coder.com>

 favicon: Add dark mode support

Closes #2538

Works as expected on latest Firefox and Chromium.

It requires git-lfs to pull down if you want to adjust the favicon and
also the affinity designer software available only on Windows and Mac.

Might be a good idea to switch to Figma at some point and commit a
.fig file.