Collect all locale (language packs) contributions in a single file

[sandy081]

Ref: #39178

Collect all locale (language packs) contributions from installed extensions in a single file called languagepacks.json.

Update the file when language pack extension is installed or uninstalled.

This file is located under user data directory.

Format of this file:

{
	"br": [
		{
			"extensionIdentifier": {
				"id": "pub.name",
				"uuid": null
			},
			"path": "<extensions-dir>/test-extension/br.tsfx"
		}
	]
}

CC @dbaeumer @aeschli