[Turbofan] Refactor GapResolver tests in preparation for FP aliasing.

- Changes tests to canonicalize FP slot/register moves, to simplify
testing any implementations that may fragment FP register moves.
- Adds code to generate correct ParallelMoves (e.g. no slot sources
of different reps overlapping.)
- Refactors test functions, so we can add manually generated tests
to current fuzzed tests.
- Adds SIMD operands, since these can be tested here now.

LOG=N
BUG=v8:4124

Review-Url: https://codereview.chromium.org/2365983002
Cr-Commit-Position: refs/heads/master@{#39943}