Add AndroidManifest and related classes for new manifest merging implementation

AndroidManifest represents a new class to handle decoupled Android manifest
processing (as opposed to the existing ApplicationManifest, which handles
manifests, resources, and assets all together). This new manifest processing
pipeline will be used by the Skylark Android Data API.

AndroidManifest wraps the manifest and related information, so we don't just
pass around untyped Artifacts all the time. Additionally, the
StampedAndroidManifest subclass explicitly states that a manifest has been
stamped with the correct package (previous confusion between passing around the
stamped and unstamped manifests has led to bugs in Blaze).

Unlike the old manifest processing pipeline, AndroidManifest:

- Does not support the old legacy manifest merger
- Is decoupled from resource and asset processing
- Does incremental merges
- Always has the package defined at analysis time
- Can be run without an input manifest (for rules which don't specify their own
  manifest but either inherit manifests that should be merged or to provide a
  dummy manifest for tooling)

RELNOTES: none
PiperOrigin-RevId: 190119992