feat(@formatjs/cli): modify output JSON schema

BREAKING CHANGE: The old output JSON messages used to be a
`MessageDescriptor[]`. This format isn't friendly to translation vendors
so we've changed it to `Record<string, Omit<MessageDescriptor, 'id'>>`.
For example:
```json
{
  "fjk13": {
    "defaultMessage": "a message",
    "description": "a description",
    "start": 0,
    "end": 20
  }
}
```

packages/cli/src/extract.ts

@@ -148,7 +148,12 @@ ${JSON.stringify(message, undefined, 2)}`
       extractedMessages.set(id, message);
     }
   }
-  const results = Array.from(extractedMessages.values());
+  const results: Record<string, Omit<MessageDescriptor, 'id'>> = {};
+  const messages = Array.from(extractedMessages.values());
+  for (const {id, ...msg} of messages) {
+    results[id] = msg;
+  }
+
   if (outFile) {
     outputJSONSync(outFile, results, {
       spaces: 2,

packages/cli/tests/extract/__snapshots__/unit.test.ts.snap

@@ -7,6 +7,8 @@ Array [
     Object {
       "compilerOptions": Object {
         "allowJs": true,
+        "noEmit": true,
+        "target": 99,
       },
       "fileName": "file1.js",
       "transformers": Object {
@@ -21,6 +23,8 @@ Array [
     Object {
       "compilerOptions": Object {
         "allowJs": true,
+        "noEmit": true,
+        "target": 99,
       },
       "fileName": "file2.tsx",
       "transformers": Object {