PLS: enforce rules around color attachment 0. Generate INVALID_OPERATION during draw calls if the following two rules are not satisfied: 1. If the fragment shader declares index zero output, then attachment zero must be present, and have a compatible numeric type. 2. If attachment zero is present, it must be enabled. This avoids complex and error-prone workarounds on macOS with AMD GPUs, and enforces the same simple and consistent rules on all platforms. Bug: angleproject:402810076 Change-Id: If029f677ca645060b8e7c2c4040e8a26d2aa2eb5 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6937659 Reviewed-by: Chris Dalton <chris@rive.app> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>