Add new common module

[CedNaru]

Currently, the godot-library module has a dependency on tools-common (string operations and some constant).
I move those dependencies to a new common module now used by godot-library and tools-common.

I also decided to move the utils package from godot-library to this new module. This serves as a first step toward making the API split easier.
So far the plan is to have a 4 module chain Common => Internal => Core => API, it means that I need a bunch of utilities in that common module. To that end, I also created a new "interop" package with basic logic to handle C++ pointers.

The number of line changes is scary but it's 99% just renames and package updates.
The only new stuff is the module itself + its "interop" package.