ref: gl: add r_showtextures implementation by ncuxonaT #2329

Job	Run time
flatpak (su.xash.Engine.Compat.i386)	3m 39s
build (ubuntu-20.04, linux, amd64)	3m 6s
build (ubuntu-20.04, linux, i386)	2m 46s
build (ubuntu-20.04, android, multiarch)	5m 3s
build (ubuntu-latest, nswitch, arm64)	3m 44s
build (ubuntu-latest, psvita, armv7hf)	2m 22s
build (windows-latest, win32, amd64)	1m 0s
build (windows-2019, win32, i386)	1m 20s
build (macos-14, apple, arm64)	1m 32s
build (macos-12, apple, amd64)	1m 39s
Upload releases	45s
	26m 56s

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