Vulkan: Implement EXT_clear_texture * Added new functions to TextureVk to clear the image. * clearImage() * clearSubImage() * Both implemented via clearSubImageImpl(), with the former a special case of the latter. * For multisample or renderable images, stagePartialClear() from ImageHelper is called to add the update. * For single-sampled non-renderable images, a buffer is filled with the pixel data and applied to the image as a buffer update. * Added new update type: ClearPartial * Used for renderable textures. This includes multisample textures. * LOAD_OP_CLEAR is used in a render pass to perform the clear. * UtilsVk::clearTexture() * (Uses ClearTextureParameters) * Uses the following functions to get the VkClearValue from the input data and format: * GetVkClearColorValueFromBytes() * GetVkClearDepthStencilValueFromBytes() * ClearPartial updates can also be superseded and removed similar to Buffer updates. * Updated UtilsVk::startRenderPass() to accept a VkClearValue* as an input arg. If used, the render pass will use LOAD_OP_CLEAR. * Enabled the feature "clearTextureEXT" on Vulkan. * Added new unit tests in ClearTextureEXTTest for various formats and pixel sizes. * Added related multisample tests in FramebufferTest.cpp. * FramebufferTest_ES31.ClearTextureEXT* * Disabled some of the new tests failing using OpenGL. * Disabled stencil-only-related tests on Pineapple. Bug: angleproject:42266869 Change-Id: I89c631d68a4ed63d9991abe1783333255ade20dd Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5778348 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Amirali Abdolrashidi <abdolrashidi@google.com>