[DebugInfo][RemoveDIs] Final final test-maintenence patch (#80988)

This should be the final portion of shaping-up the test suite to be
ready for turning on non-intrinsic debug-info:
* Pin CostModel tests that expect to see intrinsics in their -debug
output to not use RemoveDIs. This is a spurious test output difference.
* Add 'tail' to a bunch of intrinsics in UpdateTestChecks. We're
cannonicalising intrinsics to be printed with "tail" in RemoveDI
conversion as dbg.values usually pick that up while being optimised.
This is another spurious output difference.
* The "DebugInfoDrop" pass used in the debugify unit-tests happens to
operate inside the pass manager, thus it sees non-intrinsic debug-info.
Update it to correctly drop it.