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/gpui/src/text_system/font_features.rs

@@ -143,7 +143,8 @@ impl JsonSchema for FontFeatures {
                     "minimum": 0,
                     "multipleOf": 1
                 }
-            }
+            },
+            "additionalProperties": false
         })
     }
 }