Disable rasterizer discard during CopyTextureCHROMIUM.

Otherwise if the user sets this state, the copy command would be
silently skipped.

It did not seem practical to implement the large-scale refactor
suggested in the bug report to avoid setting the texture's level as
cleared.

Integrated modified version of the test case from the bug report.

Co-authored with jetski-cli.

Fixed: 500138014
Change-Id: I24c8ddbcfb19e4fadec85bec9f407bde091db8b5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7798563
Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
Auto-Submit: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1621709}