Feature request: buck2 vscode extension

(This is totally not meant as a "do this today" thing, but a placeholder here for future possible work.)

It would be nice for there to be a Buck2 vscode extension. Syntax highlighting for Buck2-flavored Starlark, support for running buck2 commands later on, maybe some nice auto-import, that kind of stuff.

The [official Bazel VSCode extension](https://marketplace.visualstudio.com/items?itemName=BazelBuild.vscode-bazel) is similar enough to actually cause interesting problems. Namely, that, right now, popping open a Buck2 Skylark `.bzl` file will trigger the loading of the Bazel extension which will, in turn, emit errors and such about missing WORKSPACE files and so on that are irrelevant in Buck2-land.

It'd be nice to get Starlark syntax highlighting, at least, without the noise, even if we don't get all the rest.