Fix some wit-bindgen-related issues with generated bindings (#5692)

* Prefix component-bindgen-generated-functions with `call_`

This fixes clashes between Rust-native methods and the methods
themselves. For example right now `new` is a Rust-generated function for
constructing the wrapper but this can conflict with a world-exported
function called `new`.

Closes #5585

* Fix types being both shared and owned

This refactors some inherited cruft from the original `wit-bindgen`
repository to be more Wasmtime-specific and fixes a codegen case where
a type was used in both a shared and an owned context.

Closes #5688

crates/component-macro/tests/codegen/function-new.wit

@@ -0,0 +1,3 @@
+default world foo {
+  export new: func()
+}