Use the vertex conversion pipeline in VertexArrayVk to detect
static vertex data and convert float32 vertices to float16. This
feature is useful for determining if an allication is vertex
bandwidth bound and seeing what gains could be had by using smaller
attributes.

This feature could be implemented in ANGLE's frontend but new
infrastructure for converting and storing the converted attributes
would need to be added to gl::VertexArray. Our backends already
have the functionality needed to handle unsupported attribute formats
and this can be repurposed for compressing vertex formats.

Bug: b/167404532
Bug: b/161716126
Change-Id: I9a09656a72e8499faa4124adf876d7261c8341c9
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2342285
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>