This change simplifies the implementation of GetBoundBufferAvailableSize
and replaces GetShaderBufferBindingSize in ProgramExecutableVk.cpp

Bug: angleproject:3573
Change-Id: I811e616989560ed74f88377742ddbb73e14b218c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2542862
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>