languages: Remove a eager conversion from LanguageName to String (#35667)

This PR changes the signature of `language_names` from

```rust
pub fn language_names(&self) -> Vec<String>
// Into
pub fn language_names(&self) -> Vec<LanguageName>
```

The function previously eagerly converted `LanguageName`'s to
`String`'s, which requires the reallocation of all of the elements. The
functions get called in many places in the code base, but only one of
which actually requires the conversion to a `String`. In one case it
would do a `SharedString` -> `String` -> `SharedString` conversion,
which is now totally bypassed.

Release Notes:

- N/A

crates/language/src/language.rs

@@ -2353,9 +2353,9 @@ mod tests {
         assert_eq!(
             languages.language_names(),
             &[
-                "JSON".to_string(),
-                "Plain Text".to_string(),
-                "Rust".to_string(),
+                LanguageName::new("JSON"),
+                LanguageName::new("Plain Text"),
+                LanguageName::new("Rust"),
             ]
         );
 
@@ -2366,9 +2366,9 @@ mod tests {
         assert_eq!(
             languages.language_names(),
             &[
-                "JSON".to_string(),
-                "Plain Text".to_string(),
-                "Rust".to_string(),
+                LanguageName::new("JSON"),
+                LanguageName::new("Plain Text"),
+                LanguageName::new("Rust"),
             ]
         );
 
@@ -2379,9 +2379,9 @@ mod tests {
         assert_eq!(
             languages.language_names(),
             &[
-                "JSON".to_string(),
-                "Plain Text".to_string(),
-                "Rust".to_string(),
+                LanguageName::new("JSON"),
+                LanguageName::new("Plain Text"),
+                LanguageName::new("Rust"),
             ]
         );