Support the new Kotlin IR backend

[Bencodes]

In order to support Jetpack Compose we need to support enabling the experimental IR backend.

Compose setup examples: https://developer.android.com/jetpack/androidx/releases/compose#declaring_dependencies
Docs for the new IR backend: https://kotlinlang.org/docs/reference/whatsnew14.html#new-jvm-ir-backend

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[Bencodes]

@googlebot I signed it!

[restingbull]

That's it? We don't need extra libs or some such?

[Bencodes]

The extra libs that are needed can be provided via compiler plugins

[restingbull]

For IR or compose?

[Bencodes]

For compose. The new IR backend is just the new compiler backend that Jetbrains has been working on. Jetpack Compose is a compiler plugin that was built to leverage the new backend (enabled via -Xplugin=... or kt_compiler_plugin(...).