feat(chunking): implement holistic chunking mechanism

[badmonster0]

Originated from #573, but this is a overall redesign of the SplitRecursively function.

• Allow users to specify a min_chunk_size
• Holistically planning the way of chunking to minimize "cost", considering the following factors
  • AST structural level
  • Literal styles (new lines, double new lines)
  • Efficiency of overlap leverage
• Also for non-dividable elements (e.g. large comments, large strings), fallback to regexp based text chunking