winch: Introduce winch-environ (#6017)

This commit introduces the `winch-environ` crate. This crate's responsibility is
to provide a shared implementatation of the `winch_codegen::FuncEnv` trait,
which is Winch's function compilation environment, used to resolve module and
runtime specific information needed by the code generation, such as resolving
all the details about a callee in a WebAssembly module, or resolving specific
information from the `VMContext`.

As of this change, the implementation only includes the necessary pieces to
resolve a function callee in a WebAssembly module. The idea is to evolve the
`winch_codegen::FuncEnv` trait as we evolve Winch's code generation.

winch/codegen/src/lib.rs

@@ -8,6 +8,7 @@
 
 mod abi;
 mod codegen;
+pub use codegen::{Callee, FuncEnv};
 mod frame;
 pub mod isa;
 pub use isa::*;