Don't prepend the worktree root when using an absolute path from
`Worktree::which`, since that does the wrong thing when running in
wasmtime given two Windows absolute paths. Also don't pass this path to
`node`, since when npm installed it's a sh/cmd wrapper not a JS file.

Part of #39153, also needs a fix on the vscode-langservers-extracted
side (missing shebang for the vscode-html-language-server script).

Release Notes:

- Fixed Zed failing to run the HTML language server in some cases.