Update to 1.21

[AbsolemJackdaw]

ash is kept in 20.6.2, as a Forge version does not exist.
Update ResourceLocation to use it's classes static methods.
Update verisoning in gradle properties
Update gradle wrapper to more recent version
Update fabric loom snapshot to more recent version
Update outdated methodname in a mixin

[jackjt8]

I have built and tested this on PR on Fabric and it doesn't appear to be working and is instead leading to a crash.

ash_api 20.6.2, fabric_api 0.105.0+1.21.1

It's possible I have made a mistake while attempting to test this PR as it's the first time I've built Transparent.

java.lang.RuntimeException: Could not execute entrypoint stage 'client' due to errors, provided by 'transparent' at 'com.diontryban.transparent.client.TransparentClientFabric'!
	at net.fabricmc.loader.impl.FabricLoaderImpl.lambda$invokeEntrypoints$2(FabricLoaderImpl.java:403)
	at net.fabricmc.loader.impl.util.ExceptionUtil.gatherExceptions(ExceptionUtil.java:33)
	at net.fabricmc.loader.impl.FabricLoaderImpl.invokeEntrypoints(FabricLoaderImpl.java:401)
	at net.fabricmc.loader.impl.game.minecraft.Hooks.startClient(Hooks.java:53)
	at net.minecraft.class_310.<init>(class_310.java:477)
	at net.minecraft.client.main.Main.main(Main.java:239)
	at net.fabricmc.loader.impl.game.minecraft.MinecraftGameProvider.launch(MinecraftGameProvider.java:480)
	at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:74)
	at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23)
	at org.prismlauncher.launcher.impl.StandardLauncher.launch(StandardLauncher.java:100)
	at org.prismlauncher.EntryPoint.listen(EntryPoint.java:129)
	at org.prismlauncher.EntryPoint.main(EntryPoint.java:70)
Caused by: java.lang.NoSuchMethodError: 'void net.minecraft.class_2960.<init>(java.lang.String)'
	at com.diontryban.ash_api.resources.ResourceLoaderFabric$1.getFabricId(ResourceLoaderFabric.java:61)
	at net.fabricmc.fabric.impl.resource.loader.ResourceManagerHelperImpl$SimpleResourceReloaderFactory.id(ResourceManagerHelperImpl.java:286)
	at net.fabricmc.fabric.impl.resource.loader.ResourceManagerHelperImpl.registerReloadListener(ResourceManagerHelperImpl.java:267)
	at net.fabricmc.fabric.impl.resource.loader.ResourceManagerHelperImpl.registerReloadListener(ResourceManagerHelperImpl.java:254)
	at com.diontryban.ash_api.resources.ResourceLoaderFabric.registerReloadListener(ResourceLoaderFabric.java:58)
	at com.diontryban.transparent.client.TransparentClient.onInitializeClient(TransparentClient.java:39)
	at com.diontryban.ash_api.modloader.FabricClientModInitializer.onInitializeClient(FabricClientModInitializer.java:44)
	at net.fabricmc.loader.impl.FabricLoaderImpl.invokeEntrypoints(FabricLoaderImpl.java:399)
	... 9 more