Vulkan: fix crash when clearing stencil with ClearBuffer Follow up to [1] which fixed a crash with glClear, but the bug remained with glClearBufferiv. This change refactors the "is stencil write masked out" query to always take the framebuffer's stencil bit count into account (practically always 8), which also happens to make the rest of the code checking this query more accurate in the presence of nonsense masks where the bottom 8 bits are 0. [1]: https://chromium-review.googlesource.com/c/angle/angle/+/3315158 Bug: chromium:40207259 Bug: angleproject:42266334 Change-Id: I68a6b0b75c67ed2cdc8c4d03b243efe5495efce1 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5889788 Reviewed-by: Geoff Lang <geofflang@chromium.org> Auto-Submit: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>