[#300] Reapply optimizer stages until fixpoint

Description

Problem: optimizer doesn't revisit nodes, hence while there might be new optimization opportunities lower in the AST uncovered by optimizations higher in the AST, optimizer won't see those.

Solution: A bit ad-hoc, but at least it's simple. Reapply each optimizer stage until the output stops changing, up to a maximum number of iterations (to avoid going into infinite loops with contradictory rules; our default rules apparently aren't, but since we allow extending the ruleset, it seems like a good idea to do this)

Problem: Meta and WithLoc wrappers preclude some optimizations and those aren't meaningful for the optimized contract anyway.

Solution: Drop these wrappers during optimization.

Related issue(s)

Resolves #300 (closed)

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