Clean the initial Rust AST implementation

[mwu-tow]

Summary

Clean-up the code, remove not needed parts, organize common libraries.

Value

The code should be nice and clean, before we start adding more functionalities into it.

Specification

All parts that were carried over from basegl without need are removed.
Common libraries are properly split and placed in the proper location.

Acceptance Criteria & Test Cases

The code with AST is merged to master, having successfully passed the reviews.