chore: Extract languages from zed crate (#8270)

- Moves languages module from `zed` into a separate crate. That way we
have less of a long pole at the end of compilation.
- Removes moot dependencies on editor/picker. This is totally harmless
and might help in the future if we decide to decouple picker from
editor.

Before:
```
Number of crates that depend on 'picker' but not on 'editor': 1
Total number of crates that depend on 'picker': 13
Total number of crates that depend on 'editor': 30
```
After:
```
Number of crates that depend on 'picker' but not on 'editor': 5
Total number of crates that depend on 'picker': 12
Total number of crates that depend on 'editor': 26
```
The more crates depend on just picker but not editor, the better in that
case.

Release Notes:

- N/A

crates/languages/src/rust/embedding.scm

@@ -0,0 +1,32 @@
+(
+    [(line_comment) (attribute_item)]* @context
+    .
+    [
+
+        (struct_item
+            name: (_) @name)
+
+        (enum_item
+            name: (_) @name)
+
+        (impl_item
+            trait: (_)? @name
+            "for"? @name
+            type: (_) @name)
+
+        (trait_item
+            name: (_) @name)
+
+        (function_item
+            name: (_) @name
+            body: (block
+                "{" @keep
+                "}" @keep) @collapse)
+
+        (macro_definition
+            name: (_) @name)
+        ] @item
+    )
+
+(attribute_item) @collapse
+(use_declaration) @collapse