Extract HTML support into an extension (#10130)

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

Release Notes:

- Removed built-in support for HTML, in favor of making it available as
an extension. The HTML extension will be suggested for download when you
open a `.html`, `.htm`, or `.shtml` file.

crates/extensions_ui/src/extension_suggest.rs

@@ -39,6 +39,9 @@ fn suggested_extensions() -> &'static HashMap<&'static str, Arc<str>> {
             ("graphql", "gql"),
             ("graphql", "graphql"),
             ("haskell", "hs"),
+            ("html", "htm"),
+            ("html", "html"),
+            ("html", "shtml"),
             ("java", "java"),
             ("kotlin", "kt"),
             ("latex", "tex"),