Deny unknown keys in settings in JSON schema so user gets warnings but settings still parses (#30583)

Closes #ISSUE

Release Notes:

- Improved checking of Zed settings so that unrecognized keys show
warnings while editing them

crates/language/src/language_settings.rs

@@ -381,6 +381,7 @@ fn default_lsp_fetch_timeout_ms() -> u64 {
 
 /// The settings for a particular language.
 #[derive(Debug, Clone, Default, PartialEq, Serialize, Deserialize, JsonSchema)]
+#[schemars(deny_unknown_fields)]
 pub struct LanguageSettingsContent {
     /// How many columns a tab should occupy.
     ///