This includes two CLs, cherry picked and squashed together:

Add texture offset attributess for D3D texture pbuffer surfaces

Add EGL_TEXTURE_OFFSET_X_ANGLE and EGL_TEXTURE_OFFSET_Y_ANGLE attributes
to EGL_ANGLE_d3d_texture_client_buffer which are used to specify offsets
used for rendering into the pbuffer surface backed by a D3D11 texture.
Rendering with the correct offset is needed when Chrome gets a texture
and offset from an external source e.g. when calling BeginDraw() on
IDCompositionSurface.

Bug: angleproject:2997
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2186176Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>
(cherry picked from commit 4b225c70)

Use surface texture offset for clears and blits

https://chromium-review.googlesource.com/c/angle/angle/+/2186176 added
surface texture offset attributes for D3D11 pbuffer surfaces, but the
implementation didn't apply the offset to blits or clears. This CL fixes
that and includes a unit test for blit, clear, and draw.

Also renames textureOffset to surfaceTextureOffset throughout since it's
clearer, and fixes the dcomp surface test to specify the update offset
returned by dcomp BeginDraw().

Bug: angleproject:2997
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2210967
Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
(cherry picked from commit 3d5f0c82)
Change-Id: If850aadedf1edaacea63113c8b6b474c156e9fa6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2237352Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>