transpile: Refactor and improve address-of handling

[Rua]

• Depends on transpile: Deep comparison of types in make_cast #1984
• Depends on transpile: Conservatively disallow mutable lvalues inside macros #1989

This PR does a few things that more or less depend on each other:

• Using ptr::from_ref, which is now available in the currently used nightly. It's still unstable there, but it's stable in Rust 2024 so it shouldn't be much of an issue to use it?
• When mutable borrows are done in a const context, only do an immutable borrow first if the edition isn't 2024. The feature that allowed mutable borrows in const context was stabilised before the 2024 edition.
• Changing how convert_address_of_common handles casting after the borrow operation. It now deep-compares the pointee types and casts only if actually needed.
• Some refactoring and cleanup, including removal of decay_ref. It was a bit of a deadweight anyway since address-of was changed to use raw borrows. Using from_ref makes it completely unnecessary.