- Fixes a crash with glTexBuffer given 0 as buffer.
- Fixes query of TEXTURE_BUFFER_SIZE.  If glTexBuffer is used to bind a
  buffer, and the buffer is modified, the result of this query must
  adapt to the new buffer size.  The spec mentions that unlike Desktop
  GL, ES doesn't have immutable buffers, and so they had no choice but
  to allow mutable buffers.

Bug: angleproject:3573
Test: KHR-GLES31.core.texture_buffer.texture_buffer_parameters
Test: dEQP-GLES31.functional.texture.texture_buffer.state_query.texture_buffer_size_integer
Change-Id: Iec77c14ccf0e9ee11a171dbe2c7386678304bcc8
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2533494
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>