resourceloader: Change 'packageFiles' format to be JSON-compatible

resourceloader: Change 'packageFiles' format to be JSON-compatible

The module definition format for 'packageFiles', as initially designed,
mixes sequential and associative arrays. This works in PHP, but not in
JSON. To make the format JSON compatible, use a 'name' key instead of
using the key in the main array.

Leave backwards compatibility in place so that extensions using the old
format can be migrated. This will be removed in the next commit.

Before:

'packageFiles' => [
	'script.js',
	'script2.js',
	'config.json' => [ 'config' => [ 'Foo', 'Bar' ] ],
	'data.json' => [ 'callback' => function () { ... } ],
],

After:

'packageFiles' => [
	'script.js',
	'script2.js',
	[ 'name' => 'config.json', 'config' => [ 'Foo', 'Bar' ] ],
	[ 'name' => 'data.json', 'callback' => function () { ... } ],
],

This can then be written in extension.json as:
"packageFiles": [
	"script.js",
	"script2.js",
	[ "name": "config.json", "config": [ "Foo", "Bar" ] ],
	[ "name": "data.json", "callback: [ "MyExtHooks", "getData" ] ]
]

Change-Id: Ic566a1cd7efd075c380bc50ba0cc2c329a2041d7