op.py refactor & improved TP support

[a-alveyblanc]

This is a large set of changes, so here are some patch notes:

Changes from refactor:

• Construct all operators using sufficiently accurate quadrature
• Separate operator construction (matrices.py) from operator application (op.py)
• Add utilities to support new operator construction methods
  • Getting basis, nodes, quadrature rules, etc. based on discretization type
• Remove FirstAxisIsElementsTag usage in op.py
  • This can be reversed if necessary, but it's a fate that was decided for upstream grudge

Changes related to TP elements:

• Add algebraic DAG transformations for fast operator evaluation with TP elements
• Add subclass of FusionContractorArrayContext with TP DAG transformations
  • use_tp_transforms kwarg to toggle on and off based on discretization type
• Add toggle for fast operator evaluation (defaults to on unless overintegration is requested)

Overintegration will require a slight fix to modepy: inducer/modepy#111