Allow serializing all cranelift-module data structures (#6172)

* Remove ModuleCompiledFunction

The same information can be retrieved using

ctx.compiled_code().unwrap().code_info().total_size

In addition for Module implementations that don't immediately compile the
given function there is no correct value that can be returned.

* Don't give anonymous functions and data objects an internal name

This internal name can conflict if a module is serialized and then
deserialized into another module. It also wasn't used by any of the
Module implementations anyway.

* Allow serializing all cranelift-module data structures

This allows a Module implementation to serialize it's internal state and
deserialize it in another compilation session. For example to implement
LTO or to load the module into cranelift-interpreter.

* Use expect

cranelift/module/Cargo.toml

@@ -15,11 +15,15 @@ cranelift-codegen = { workspace = true }
 cranelift-control = { workspace = true }
 hashbrown = { workspace = true, optional = true }
 anyhow = { workspace = true }
+serde = { version = "1.0.94", features = ["derive"], optional = true }
 
 [features]
 default = ["std"]
 std = ["cranelift-codegen/std"]
 core = ["hashbrown", "cranelift-codegen/core"]
 
+# For dependent crates that want to serialize some parts of cranelift
+enable-serde = ["serde", "cranelift-codegen/enable-serde"]
+
 [badges]
 maintenance = { status = "experimental" }