Some syntactic cleanup

Mostly, this change renames HeadTrackingMode to
SpatializerHeadTrackingMode in order to avoid name collision with the
HeadTrackingMode type from libheadtracking.

Other nits are included.

Test: m -j
Bug: 188502620
Change-Id: I7f4188c1f401a98044f28c68d9613267d5baa808
5 files changed