Removes duplicate code in src/obj.rs, crates/obj and crates/jit/object.rs (#1993)

Changes:

 -  Moves object creation code from crates/jit/object.rs to the creates/obj (as ObjectBuilder)
 -   Removes legacy crates/obj/function.rs
 -  Removes write_debugsections

crates/obj/src/lib.rs

@@ -23,12 +23,13 @@
     )
 )]
 
+mod builder;
 mod context;
 mod data_segment;
-mod function;
 mod module;
 mod table;
 
+pub use crate::builder::{utils, ObjectBuilder, ObjectBuilderTarget};
 pub use crate::module::emit_module;
 
 /// Version number of this crate.