fs_mgr: Move libfiemap into libfs_mgr, and introduce libfs_mgr_binder.

This eliminates libfiemap as a standalone library and instead bundles it
into libfs_mgr. All consumers of libfiemap need libfs_mgr, and having
them tightly coupled reduces linkage complexity.

When to use libfs_mgr: In recovery, first-stage-init, or when libfiemap
or overlayfs is not used.

When to use libfs_mgr_binder: When not in recovery/first-stage init, and
overlayfs or libfiemap is needed. In this case, IImageManager will proxy
over binder to gsid.

Bug: 134949511
Test: builds, fiemap_writer/image_test passes.
Change-Id: I4c1a5698afdbf9b3bf87accec98254c1fb6f4e0e