Add fast operator evaluation for tensor-product discretizations

[a-alveyblanc]

Supersedes #313, #354

Adds:

• Fast operator evaluation for tensor-product discretizations
• Metadata (tags) relevant to tensor-product discretizations used during (eager and lazy) compilation
• WADG + Overintegration (+ fast operator evaluation in the case of tensor-product elts)

Non-essential transformations will be added in a later PR. This is to keep this (already large) PR manageable.

TODOs:

• Gradient
  • Strong form
  • Weak form
• Divergence
  • Strong form
  • Weak form
• Mass
• Inverse mass
• Support overintegration + fast operator evaluation
• Face mass
• Add generic bilinear form evaluation
• Rewrite op.py to use generic bilinear form evaluation

cc @MTCam

[inducer]

Should this be marked draft given that there are pending TODOs?

[inducer]

Suggested change

	tagged=(FirstAxisIsElementsTag(),
	OutputIsTensorProductDOFArrayOrdered(),),
	tagged=(FirstAxisIsElementsTag(),
	OutputIsTensorProductDOFArrayOrdered(),),

buh-bye!