[SCEV] Use or disjoint flag (#74467)

Use the disjoint flag to convert or to add instead of calling the
haveNoCommonBitsSet() ValueTracking query. This ensures that we can
reliably undo add -> or canonicalization, even in cases where the
necessary information has been lost or is too complex to reinfer in
SCEV.

I have updated the bulk of the test coverage to add the necessary
disjoint flags in advance.