devel/librashader: update to 0.5.1

Changes:
https://github.com/SnowflakePowered/librashader/releases/tag/librashader-v0.5.0
https://github.com/SnowflakePowered/librashader/releases/tag/librashader-v0.5.1

Version 0.5.0 bumps the ABI to 2, and is thus ABI-incompatible with versions of
librashader prior to 0.5.0. Trying to load this version of librashader will fail
if the application only supports ABI 1.

Upstream's librashader-build-script doesn't do more than to compile the package
librashader-capi and to move the resulting files around. Therefore the port uses
the standard do-build target from the ports framework by setting CARGO_FEATURES
and CARGO_BUILD_ARGS appropriately instead.

This standardization also allows us to drop the DEBUG port option. Generating a
debug build is now controlled by setting WITH_DEBUG, see also Mk/Uses/cargo.mk.

The port now only compiles the OpenGL and Vulkan runtimes by specifying the
appropriate CARGO_FEATURES. This excludes compiling the unneeded Metal and
DirectX runtimes.

PR: 282547
MFH: no (ABI break)