Multidimensional dense workspaces

[weiya711]

1. Add in functionality for multi-dimensional dense workspaces
2. Also add in multi-dimensional dense workspaces for the TACO command-line tool.
3. Fix the precompute(...) concrete index notation transformation algorithm to be similar to the one in the TACO workspaces paper.
4. Add in ir::Stmt workspace_rewriter to allow for multi-dimensional dense workspace lowering. This rewriter rewrites the lowered ir::Stmt to replace all workspace GetProperty(..., Dimension) nodes with the correct ir::Expr corresponding to the workspace size for that mode.
5. Add in more workspace regression tests in test/tests-workspaces.cpp

This does not break any of the GPU tests (see https://github.com/tensor-compiler/taco/actions/runs/955323370)

Note: Some *Scheduled(...) (like concretizeScheduled(), isReductionNotationScheduled(), etc.) methods in src/index_notation/index_notation.cpp are not currently being used but should be useful in the future. They were originally created for another version of the precompute(...) transformation algorithm, but are no longer needed there. I would still like to add them in to master along with this PR since there are still scenarios where the compiler needs to concretize an Einsum notation assignment with a ProvenanceGraph into its corresponding post-scheduled concrete index notation statement.