Perform algebraic simplification in Simplify
Perform algebraic simplification in Simplify

Computing the size of `Fin n` for a known constant `n` takes three
instructions that can be constant folded. It used to happen when
`indexSetSize` was implemnted in the compiler using the builder methods,
but it's not happening for the current implementation in user-space!

The simple redirection of simplified ops through relevant builder
methods closes the gap again (and interestingly enough speeds up our
compilation quite a bit in certain scenarios).

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