Cleanup #115269: GPU: texture view usage flags

Texture usage flag `GPU_TEXTURE_USAGE_MIP_SWIZZLE_VIEW`
was originally implemented and used too conservatively for many
cases in which the underlying API flags were not required.

Renaming to `GPU_TEXTURE_USAGE_FORMAT_VIEW` to reflect
the only essential use case for when a texture view is initialized with
a different texture format to the source texture. Texture views can
still be created without this flag when mip range or base level is
adjusted,

This flag is still required by stencil views and internally by the Metal
backend for certain feature support such as SRGB render toggling.

Patch also includes some small changes to the Metal backend to
adapt to this new compatibility and correctly capture all texture view
use-cases.

Authored by Apple: Michael Parkin-White

@@ -472,3 +472,1 @@
-  BLI_assert_msg(
-      GPU_texture_usage(src) & GPU_TEXTURE_USAGE_MIP_SWIZZLE_VIEW,
-      "Source texture of TextureView must have GPU_TEXTURE_USAGE_MIP_SWIZZLE_VIEW usage flag.");
+  BLI_assert_msg((format == GPU_texture_format(src)) ||