viz: Flatten dc_layer_overlay.cc FromTextureQuad into FromDrawQuad

After the removal of YUVVideoDrawQuad, it's no longer useful to have a
separate method to create a TextureDrawQuad. The ValidateDrawQuad case
was not flattened since ValidateTextureQuad affects control flow.

Change-Id: I085a0c9334ee125835b85e9c2bdd3a5656a8237a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6006255
Commit-Queue: Michael Tang <tangm@microsoft.com>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Reviewed-by: Rafael Cintron <rafael.cintron@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1381818}