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.

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

[hansihe]

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