[mlir][sparse] Preliminary code changes for ExprId, LatPointId, LatSetId newtypes

This commit contains several code changes which are ultimately required for converting the varions `Merger` identifiers from typedefs to newtypes.  The actual implementation of the newtypes themselves has been split off into separate commits, in hopes of simplifying the review process.

Depends On D146561

Reviewed By: aartbik

Differential Revision: https://reviews.llvm.org/D146684