Chromium enables a custom extension, GL_CHROMIUM_texture_filtering, when
using SwiftShaderGL, to enable high precision filtering. This change
makes it so ANGLE also handles this same extension when using the
SwiftShaderVK backend, by enabling the new
VK_GOOGLE_sampler_filtering_precision custom extension.

Bug: b/146423360
Bug: b/154620295
Change-Id: I69cafc1ccf5970a3d220ac7e13ec3c8fdd4a9643
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2185822
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>