settings_content: Fix globally excluded language servers starting (#60984)

Closes https://github.com/zed-industries/zed/issues/60763

Follow-up to #60000. Global language server exclusions were added to
per-language settings without removing an explicit enable for the same
server, allowing it to still start.

For example, this setting should disable `vtsls` for every language:

```json
{
  "language_servers": ["!vtsls", "..."]
}
```

However, TypeScript’s default configuration explicitly enables `vtsls`,
causing it to still start.

Release Notes:

- Fixed language servers starting despite being disabled globally.

crates/settings_content/src/language.rs

@@ -67,6 +67,12 @@ impl merge_from::MergeFrom for AllLanguageSettingsContent {
             language_settings.merge_from(&other.defaults);
             if let Some(mut language_server_overrides) = language_server_overrides {
                 if let Some(disabled) = &globally_disabled_servers {
+                    for disabled_server in disabled {
+                        if let Some(enabled_server) = disabled_server.strip_prefix('!') {
+                            language_server_overrides.retain(|entry| entry != enabled_server);
+                        }
+                    }
+
                     let insert_before = language_server_overrides
                         .iter()
                         .position(|entry| entry == REST_OF_LANGUAGE_SERVERS)
@@ -1327,6 +1333,55 @@ mod test {
         );
     }
 
+    #[test]
+    fn test_global_language_server_disable_overrides_per_language_enable() {
+        let mut base = AllLanguageSettingsContent {
+            defaults: LanguageSettingsContent {
+                language_servers: Some(vec![REST_OF_LANGUAGE_SERVERS.into()]),
+                ..LanguageSettingsContent::default()
+            },
+            languages: LanguageToSettingsMap(
+                [(
+                    "TypeScript".into(),
+                    LanguageSettingsContent {
+                        language_servers: Some(vec![
+                            "!typescript-language-server".into(),
+                            "vtsls".into(),
+                            REST_OF_LANGUAGE_SERVERS.into(),
+                        ]),
+                        ..LanguageSettingsContent::default()
+                    },
+                )]
+                .into_iter()
+                .collect(),
+            ),
+            ..AllLanguageSettingsContent::default()
+        };
+
+        let user = AllLanguageSettingsContent {
+            defaults: LanguageSettingsContent {
+                language_servers: Some(vec!["!vtsls".into(), REST_OF_LANGUAGE_SERVERS.into()]),
+                ..LanguageSettingsContent::default()
+            },
+            ..AllLanguageSettingsContent::default()
+        };
+
+        base.merge_from(&user);
+
+        let expected = vec![
+            "!typescript-language-server".to_string(),
+            "!vtsls".to_string(),
+            REST_OF_LANGUAGE_SERVERS.to_string(),
+        ];
+        assert_eq!(
+            base.languages
+                .0
+                .get("TypeScript")
+                .and_then(|settings| settings.language_servers.as_deref()),
+            Some(expected.as_slice()),
+        );
+    }
+
     #[test]
     fn test_language_servers_merge_no_per_language_config_uses_global() {
         let mut base = AllLanguageSettingsContent {