[WIP] core:odin/frontend

[DragosPopse]

This is the beginning of the WIP core:odin/frontend package. I will be starting working on it tomorrow, but I want to have a high level plan here written for everyone to see, and have the progress visible for everyone to review.

Plans:

• merge core:odin/ast core:odin/parser core:odin/tokenizer under the new core:odin/frontend
• add missing checker
• Modify core:odin/ast types to include information about type checking, acording to the C++ compiler
• Do a mostly line-by-line translation of the check*.cpp files into odin code

Conversion rules (To be added as discovered):

• union + enum tag from C++ will be replaced by odin's tagged union
• StringMap replaced by map[string]T
• PtrSet replaced by map[^T]bool
• PtrMap TBD
• Any std::atomic variable will be prefixed by atomic_, as there is not a dedicated type in odin
• BlockingMutex will be sync.Mutex
• RwMutex will be sync.RW_Mutex
• RecursiveMutex will be sync.Recursive_Mutex
• Ast will be renamed to Node
• Refactor to follow odin's Ada_Case types, snake_case procs.

Missing features in core (to be added as found):

• mpsc_queue mpmc_queue: this seems to be required for some of the multithreading optimization. These can potentially be added as part of this pull request, in core:container/queue/mpsc or core:container/mpsc_queue