Add shaka namespace types to generated externs

[joeyparrish]

There are cases where we want to refer to the type of the shaka namespace in a type-safe way. For example, in test/test/util/loader.js, we load the Shaka library dynamically for tests without inserting it into the global namespace. To refer to that with strong types, we need a namespace type.

Today, we have code like in

shaka-player/test/test/util/loader.js

Lines 7 to 40 in 7bcb86e

	/**
	* A stand-in type for the "shaka" namespace. Used when loading the compiled
	* library or when referencing it in ManifestGenerator or TestScheme.
	*
	* The new compiler has a "typeof" annotation for classes, but it warns of an
	* incomplete type when used on the entire library namespace. So instead, we
	* use this type, which maps out parts of the compiled namespace used in
	* top-level integration tests.
	*
	* @typedef {{
	* Player: typeof shaka.Player,
	* media: {
	* SegmentReference: typeof shaka.media.SegmentReference,
	* InitSegmentReference: typeof shaka.media.InitSegmentReference,
	* SegmentIndex: typeof shaka.media.SegmentIndex,
	* PresentationTimeline: typeof shaka.media.PresentationTimeline
	* },
	* net: {
	* NetworkingEngine: typeof shaka.net.NetworkingEngine
	* },
	* offline: {
	* Storage: typeof shaka.offline.Storage
	* },
	* ui: {
	* Overlay: typeof shaka.ui.Overlay,
	* Controls: typeof shaka.ui.Controls,
	* Element: typeof shaka.ui.Element
	* },
	* util: {
	* StringUtils: typeof shaka.util.StringUtils
	* }
	* }}
	*/
	let shakaNamespaceType;

that creates a one-off typedef of the parts we're using in those tests. Ideally, we would generate this into our generated externs, and it would be complete.

This has also come up in context of the Cast Application Framework, which depends on Shaka Player and has unit tests that mock the Shaka API. For those tests, we would like to use the same complete, generated typedef for the namespace.