[Shared Library] Set up a shared library structure to use on both frontend and backend

[allenh]

Description

We need to have a shared library to be used on both server and frontend to compute legal piece moves.

Acceptance Criteria

1. create a shared library folder structure in the repo on the top level called shared
2. make sure server has access to /shared on local development
3. make sure frontend has access to /shared on local development
4. make sure the current build process can bundle the /shared tooling in both frontend and server images

Testing demo

1. as a demo create a simple move validation for 兵
   • eg: given current position (x, y, 1), the valid moves set is [(x+1, y, 1), (x-1,y,1)] assuming both x+1 and x-1 are within bounds