vscode build: switch to pnpm?

[tmm1]

Since the switch from yarn to npm, I have observed a ton of spurious build failures. I isolated some of these to node-gyp and sent a couple of patches.

However in my experience, npm itself is still quite slow and unreliable compared to other solutions.

Is there any appetite for switching over to pnpm? I know there is a considerable amount of build engineering work required, which I am willing to contribute but only if there is hope for getting it upstreamed.

cc https://github.com/microsoft/vscode/pull/226927 https://github.com/microsoft/vscode/issues/196795

cc @deepak1556 @joaomoreno