[//components/exo] Compute texture target to use from ClientSharedImage

exo::Buffer takes in a texture target to use and when in zero-copy mode,
passes it to a gpu::MailboxHolder that it creates. The only production
callsites that create exo::Buffer instances in zero-copy mode are at
[1] and [2] (the latter via [3][4]).

This CL changes exo::Buffer to compute the texture target from the
ClientSharedImage that was created from the passed-in GMB. This
function has identical semantics to what is currently being done, based
on the following reasoning:

* For [1], the texture target is currently being computed at [5]. This
  is exactly what ClientSharedImage::GetTextureTarget(BufferFormat)
  does.
* [2] is hardcoding the format to RGBA_8888. For RGBA_8888,
  ClientSharedImage::GetTextureTarget(BufferFormat) will always return
  GL_TEXTURE_2D on ChromeOS [6].

We leave a CHECK_EQ() for verification in going through trybots/CI. Once
this CL passes trybots/CI, we will remove exo::Buffer taking in a
texture
target altogether.

[1] https://source.chromium.org/chromium/chromium/src/+/main:components/exo/display.cc;l=130-145;drc=79fd5d71c46d0e6ecd842867bc1c787fae68e218;bpv=1;bpt=1
[2] https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/ash/app_restore/arc_ghost_window_shell_surface.cc;l=41-44;drc=79fd5d71c46d0e6ecd842867bc1c787fae68e218
[3] https://source.chromium.org/chromium/chromium/src/+/main:components/exo/buffer.cc;l=579-584;drc=79fd5d71c46d0e6ecd842867bc1c787fae68e218;bpv=1;bpt=1
[4] https://source.chromium.org/chromium/chromium/src/+/main:components/exo/buffer.cc;l=518;drc=79fd5d71c46d0e6ecd842867bc1c787fae68e218;bpv=1;bpt=1
[5] https://source.chromium.org/chromium/chromium/src/+/main:components/exo/display.cc;l=117-120;drc=79fd5d71c46d0e6ecd842867bc1c787fae68e218;bpv=1;bpt=1
[6] https://source.chromium.org/chromium/chromium/src/+/main:gpu/command_buffer/common/gpu_memory_buffer_support.cc;l=211-226?q=NativeBufferNeedsPlatf&ss=chromium

Bug: 41494843
Change-Id: I383fe6ae3276cdfed258693135a6974aeaa55990
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5359498
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1271029}