klang for generating metal interop to use it in the JVM

[soywiz]

An initial prototype was here:

• https://github.com/korlibs/korge/pull/1682 It supports generating headers at runtime via obj-c reflection APIs, though it loses type information. It is a good start since you can manually add some types, and in the end for basic AG implmentation the API usage will be limited.

@yggdrasil-io has been working on klang, that supports using clang to generate an AST that can be used to also generate interoperability code:

• https://github.com/ygdrasil-io/klang

The idea is to improve klang to generate metal headers, then include the interfaces we need to implement AG.

By using metal on the JVM, we can integrate better with the new Java versions that use Metal for rendering. Also since JVM compiles and runs super fast, we can iterate faster and implement AGMetal right, and then port it to the K/N backend with all the stuff solved.