copy-prop: Online def-use analysis for copy propagation pass

Implement an online def-use analysis for the copy propagation pass.  The
analysis is updated in an incremental fashion as changes are made to the
MIR body instead of being recomputed from scratch after each change.

The analysis is intended to be equivalent to the previous one, but it
also offers a new methods to: remove specific statement, remove storage
markers, and replace the uses of a local with another local or a
constant, all while keeping the analysis up-to date.

No functional changes intended.

Author: tmiasko