[ES UI] Reintroduce import of brace/mode/json (elastic#78571)

* added brace/mode/json import everywhere json mode is being used

* added brace mocks to tests

* slight refactor of imports

* remove import from es ui shared

* Reverse adding brace/mode/json import everywhere

- different approach of just adding brace/json/mode to
  es_ui_shared as before with a BIG comment

* updated @kbn/ace readme

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

packages/kbn-ace/README.md

@@ -1,5 +1,20 @@
 # @kbn/ace
 
-Contains all Kibana-specific brace related code. Excluding the code that still inside of Console because that code is only used inside of console at the moment.
+This package contains the XJSON mode for brace. This is an extension of the `brace/mode/json` mode.
 
-This package enables plugins to use this functionality and import it as needed -- behind an async import so that brace does not bloat the JS code needed for first page load of Kibana.
+This package also contains an import of the entire brace editor which is used for creating the custom XJSON worker.
+
+## Note to plugins
+_This code should not be eagerly loaded_.
+
+Make sure imports of this package are behind a lazy-load `import()` statement.
+
+Your plugin should already be loading application code this way in the `mount` function.
+
+## Deprecated
+
+This package is considered deprecated and will be removed in future.
+
+New and existing editor functionality should use Monaco.
+
+_Do not add new functionality to this package_. Build new functionality for Monaco and use it instead.

src/plugins/es_ui_shared/static/forms/components/index.ts

@@ -17,6 +17,21 @@
  * under the License.
  */
 
+/*
+@TODO
+
+The brace/mode/json import below is loaded eagerly - before this plugin is explicitly loaded by users. This makes
+the brace JSON mode, used for JSON syntax highlighting and grammar checking, available across all of Kibana plugins.
+
+This is not ideal because we are loading JS that is not necessary for Kibana to start, but the alternative
+is breaking JSON mode for an unknown number of ace editors across Kibana - not all components reference the underlying
+EuiCodeEditor (for instance, explicitly).
+
+Importing here is a way of preventing a more sophisticated solution to this problem since we want to, eventually,
+migrate all code editors over to Monaco. Once that is done, we should remove this import.
+ */
+import 'brace/mode/json';
+
 export * from './field';
 export * from './form_row';
 export * from './fields';