As the number of internal shaders grow, it's helpful in development time
to be able to build variations of a specific shader, instead of building
everything every time.

With this commit, one can do:

$ python gen_vk_internal_shaders.py SubString

which will result in compilation of shaders whose name matches the glob
*SubString*.

Bug: angleproject:2958
Change-Id: I3b18d7e32e2ec4317531a7655eb2c6148cea177b
Reviewed-on: https://chromium-review.googlesource.com/c/1369285
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>