Regroup JS modules features (#3669)

* Move `js-modules` group under `javascript`
* Move `import-assertions` to `js-modules` group

Author: ddbeck

features/import-assertions.yml

@@ -1,7 +1,7 @@
 name: Import assertions
 description: 'Module `import … assert { type: "json" }` and `import … assert { type: "css" }` JavaScript statements load JSON and CSS data.'
 spec: https://github.com/tc39/proposal-import-attributes/tree/abca60286360b47f9a6be25a28f489c2cb157beb
-group: javascript
+group: js-modules
 discouraged:
   reason: Import assertions are superseded by import attributes.
   removal_date: 2024-06-13

groups/js-modules.yml

@@ -1 +1,2 @@
 name: JavaScript modules
+parent: javascript