Previously we supported read only depth attachment that attachment and
sample are using the same texture. It was always assuming it will be
read only if the same texture is attached to FBO and same time bound to
texture unit. But we never supported if it actually writing to depth
texture, but at the different level with sampling. This is supported
OpenGL operation as long as the levels render to is outside [base_level,
max_level]. Later on, we added support of the above operation, but
limited to color buffers. This CL extends the same support of render and
sample to the same depth texture with non-overlapping levels. Android
game black desert mobile is running into this usage case.

Bug: b/181797383
Change-Id: I7ee1d52f27603f933102ad1b098684309449c406
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2819487
Commit-Queue: Charlie Lao <cclao@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Ian Elliott <ianelliott@google.com>