Rework the (Relocatable)Debuginfo structs

[bjorn3]

Currently RelocatableDebuginfo has a single Debuginfo entry for each memory map. This Debuginfo entry then contains a memmap::Mmap an object::File and several parsed structs derived from it. This struct is self-referential. What I imagine is that RelocatableDebuginfo becomes the self-referential type with several memmap::Mmap. One for each object file and not for each memory map. It will also contain a single Debuginfo for each object file which refers to the Mmap in RelocatableDebuginfo. RelocatableDebuginfo will then get a with method that makes it possible to add new Mmap and access/modify the Debuginfo within a closure.

This design will reduce the amount of times an object file is parsed to once. It will also allow reusing the same parsed debuginfo when memory mapa change. In addition it will eliminate the necessity of wrapper functions on Debuginfo for everything to handle the self-referentialness. Lastly it is necessary to handle dwarf unwinding, as that needs to get access to the offsets of the .text and .plt sections from within the handling of the .eh_frame section.