Refactoring/performance

[hansihe]

A lot of suboptimal things are done right now and can relatively easily be fixed to give some major performance and cleanliness improvements.

• Refactor Eir representation to use arena based allocation, improve the graph implementation.
• Refactor HIR representation to use arena based allocation
• Refactor parse tree representation to use arena based allocation
• Refactor pattern compilation passes to reduce allocations
• Refactor validation compilation passes to reduce allocations

[hansihe]

1 is fixed for Eir itself, should also he done for parse tree and hir.