Warn about unknown fields when editing settings json (#33678)

Closes #30017

* While generating the settings JSON schema, defaults all schema
definitions to reject unknown fields via `additionalProperties: false`.

* Uses `unevaluatedProperties: false` at the top level to check fields
that remain after the settings field names + release stage override
field names.

* Changes json schema version from `draft07` to `draft_2019_09` to have
support for `unevaluatedProperties`.

Release Notes:

- Added warnings for unknown fields when editing `settings.json`.

crates/language/src/language_settings.rs

@@ -410,7 +410,6 @@ 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.
     ///