Extract TOML support into an extension (#9940)

This PR extracts TOML support into an extension and removes the built-in
TOML support from Zed.

There's a small workaround necessary in order for us to set the file
permissions on the `taplo` binary so that it can be run. Eventually
we'll want to build this into the extension API, but for now we're just
hard-coding it on the host side.

Release Notes:

- Removed built-in support for TOML, in favor of making it available as
an extension. The TOML extension will be suggested for download when you
open a `.toml` or `Cargo.lock` file.