Provide wasm extensions with APIs needed for using pre-installed LSP binaries (#9085)

In this PR, we've added two new methods that LSP extensions can call:
* `shell_env()`, for retrieving the environment variables set in the
user's default shell in the worktree
* `which(command)`, for looking up paths to an executable (accounting
for the user's shell env in the worktree)

To test this out, we moved the `uiua` language support into an
extension. We went ahead and removed the built-in support, since this
language is extremely obscure. Sorry @mikayla-maki. To continue coding
in Uiua in Zed, for now you can `Add Dev Extension` from the extensions
pane, and select the `extensions/uiua` directory in the Zed repo. Very
soon, we'll support publishing these extensions so that you'll be able
to just install it normally.

Release Notes:

- N/A

---------

Co-authored-by: Marshall <marshall@zed.dev>