Rust: Handle different rust_crate_type depending on default_library

[xclaesse]

When building a C library from rust code we have to pass rust_crate_type: 'cdylib' or rust_crate_type: 'staticlib' depending if it's a shared_library() or static_library(). But in the case of both_libraries() or library() the value must be different depending on default_library option.

We probably need to add a new value rust_crate_type: 'clib' to mean cdylib if shared library, staticlib if static library.

[xclaesse]

Note that we already handle this correctly if rust_crate_type is omitted, but it default to building Rust library rlib or dylib. This raises the question: Do we even need all possible values for rust_crate_type? rlib vs dylib and cdylib vs staticlib is something meson already knows. The only thing user needs to specify is if it's a rust or c lib.

[sdroege]

There's also proc-macro, but that also needs a bit more special handling (e.g. #11702)

[sdroege]

This is handled in #11714 AFAICS?