Chrome's validating command decoder links statically with the ANGLE
translator.  This change adds a target that builds the translator with
only gl and d3d support for this purpose.  This will prevent chrome from
linking against glslang because of the Vulkan backend.  As a bonus, it
will reduce the binary size of Chrome by stipping the Vulkan and Metal
translation and transformation codes.

Bug: angleproject:5810
Change-Id: I5673bad53817ff2aa8486622ff2c64b44c77240f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2797511Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>