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/highlights.scm

@@ -0,0 +1,116 @@
+(type_identifier) @type
+(primitive_type) @type.builtin
+(self) @variable.special
+(field_identifier) @property
+
+(call_expression
+  function: [
+    (identifier) @function
+    (scoped_identifier
+      name: (identifier) @function)
+    (field_expression
+      field: (field_identifier) @function.method)
+  ])
+
+(generic_function
+  function: [
+    (identifier) @function
+    (scoped_identifier
+      name: (identifier) @function)
+    (field_expression
+      field: (field_identifier) @function.method)
+  ])
+
+(function_item name: (identifier) @function.definition)
+(function_signature_item name: (identifier) @function.definition)
+
+(macro_invocation
+  macro: [
+    (identifier) @function.special
+    (scoped_identifier
+      name: (identifier) @function.special)
+  ])
+
+(macro_definition
+  name: (identifier) @function.special.definition)
+
+; Identifier conventions
+
+; Assume uppercase names are types/enum-constructors
+((identifier) @type
+ (#match? @type "^[A-Z]"))
+
+; Assume all-caps names are constants
+((identifier) @constant
+ (#match? @constant "^_*[A-Z][A-Z\\d_]*$"))
+
+[
+  "("
+  ")"
+  "{"
+  "}"
+  "["
+  "]"
+] @punctuation.bracket
+
+(_
+  .
+  "<" @punctuation.bracket
+  ">" @punctuation.bracket)
+
+[
+  "as"
+  "async"
+  "await"
+  "break"
+  "const"
+  "continue"
+  "default"
+  "dyn"
+  "else"
+  "enum"
+  "extern"
+  "for"
+  "fn"
+  "if"
+  "in"
+  "impl"
+  "let"
+  "loop"
+  "macro_rules!"
+  "match"
+  "mod"
+  "move"
+  "pub"
+  "ref"
+  "return"
+  "static"
+  "struct"
+  "trait"
+  "type"
+  "use"
+  "where"
+  "while"
+  "union"
+  "unsafe"
+  (mutable_specifier)
+  (super)
+] @keyword
+
+[
+  (string_literal)
+  (raw_string_literal)
+  (char_literal)
+] @string
+
+[
+  (integer_literal)
+  (float_literal)
+] @number
+
+(boolean_literal) @constant
+
+[
+  (line_comment)
+  (block_comment)
+] @comment