The only reason a dispatch call may need to break the render pass
implicitly is for read-after-writes where the write originates from the
render pass but is not through a storage buffer/image.  There are only
two such scenrios possible:

- Framebuffer attachment write -> texture sample
- Transform feedback write -> ubo read

All other uses of the buffers and textures that require breaking the
render pass are handled by `glMemoryBarrier`.

Bug: angleproject:5070
Change-Id: I92b50d69d8782097ee8ff477ac57da6209c326a1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2698998
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>