Support allowSRGBInputs on Vulkan (via secondary texture views)

All textures still have a "correct" image view that matches their actual
format. For sRGB textures, we can ask for a non-sRGB view that is
created on demand (and cached), in legacy mode.

Finally, turn on sRGB support in Vulkan. The gamma GM now looks correct
in both L32 and S32.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1970293002

Review-Url: https://codereview.chromium.org/1970293002
diff --git a/src/gpu/vk/GrVkCaps.cpp b/src/gpu/vk/GrVkCaps.cpp
index 746499f..db21cc2 100644
--- a/src/gpu/vk/GrVkCaps.cpp
+++ b/src/gpu/vk/GrVkCaps.cpp
@@ -21,6 +21,7 @@
     * GrDrawTargetCaps fields
     **************************************************************************/
     fMipMapSupport = true;   // always available in Vulkan
+    fSRGBSupport = true;   // always available in Vulkan
     fNPOTTextureTileSupport = false; //TODO: figure this out
     fTwoSidedStencilSupport = true;  // always available in Vulkan
     fStencilWrapOpsSupport = false; //TODO: figure this out