Implements a fork-reshape pass in the scheduling language which can be used to coalesce a selection of fork-joins, interchange them into a specified order, and then split them into a specified series of chunks.
Adds a parallel and tiled schedule for matmul that uses fork-reshape to keep the schedule quite clean.
Also adds tuples to the scheduling language and a new form of let-statements that allow destructing tuples, it's not the nicest (it's not a general pattern handler and will only cause an error if there are too many fields on the left-hand side, not too few, but it's enough to make the code that uses fork-reshape cleaner).
Includes a few other tweaks I ran into
When adding a node in the editor, only insert an empty def_use set if the node doesn't have one yet (this is important due to cycles between nodes, and was causing issues in fork reshape since it invokes a series of passes using the same editor)
Made fork-coalesce return the fork and join nodes when it succeeds so that they can be used in further operations.
Modified fork coalesce's check for control flow between the forks and joins to check via uses rather than users because I was having weird issues with checking users
Modified fork coalesce to perform everything as a single edit because I was having issues when manually scheduling matmul when using selections with coalesce.
Modified fork split to return the ID of the new fork on a success
Modified both fork split and coalesce to propagate parallel fork schedules when appropriate to avoid having to re-assign/re-infer schedules
