In ContextVk::updateActiveTextures we end up calling this method
shouldSwitchToReadOnlyDepthFeedbackLoopMode(...) for every active
texture. Since color textures are more numerous than depth, check
the texture type beforehand to decrease function stack depth.

This removes 0.5% CPU overhead from a Manhattan30 offscreen run

Bug: angleproject:5689
Change-Id: I14758b031e58b269392b4f450a5bb1ba8edabb44
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2723493Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>