winch: Add license and update Cargo.toml (#5170)

This commit adds the appropriate license to `winch-codegen` and to
`wasmtime-winch`; it also add the authors entry to `winch-codegen`

winch/codegen/Cargo.toml

@@ -1,4 +1,5 @@
 [package]
+authors = ["The Winch Project Developers"]
 name = "winch-codegen"
 description = "Winch code generation library"
 license = "Apache-2.0 WITH LLVM-exception"