Convert compilation artifacts to just bytes (#3239)

* Convert compilation artifacts to just bytes

This commit strips the `CompilationArtifacts` type down to simply a list
of bytes. This moves all extra metadata elsewhere to live within the
list of bytes itself as `bincode`-encoded information.

Small affordance is made to avoid an in-process
serialize-then-deserialize round-trip for use cases like `Module::new`,
but otherwise this is mostly just moving some data around.

* Rename data section to `.rodata.wasm`

crates/jit/Cargo.toml

@@ -28,6 +28,7 @@ addr2line = { version = "0.16.0", default-features = false }
 libc = { version = "0.2.60", default-features = false, optional = true }
 scroll = { version = "0.10.1", features = ["derive"], optional = true }
 ittapi-rs = { version = "0.1.5", optional = true  }
+bincode = "1.2.1"
 
 [target.'cfg(target_os = "windows")'.dependencies]
 winapi = { version = "0.3.8", features = ["winnt", "impl-default"] }