Extract Zig support into an extension (#9893)

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

There's a small workaround necessary in order for us to set the file
permissions on the `zls` 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 Zig, in favor of making it available as
an extension. The Zig extension will be suggested for download when you
open a `.zig` file.

crates/extensions_ui/src/extension_suggest.rs

@@ -48,6 +48,7 @@ pub fn suggested_extension(file_extension_or_name: &str) -> Option<Arc<str>> {
                 ("swift", "swift"),
                 ("templ", "templ"),
                 ("wgsl", "wgsl"),
+                ("zig", "zig"),
             ]
             .into_iter()
             .map(|(name, file)| (file, name.into()))