[SCEV] Tighten loop guards range check idiom (#210387)
Previously, the idiom matcher derived the clamp range only from the raw
`(LHS + C1) u< C2` form and rejected wrapped or full ranges.
Intersect the derived range with the known unsigned range of `LHSUnknown`.
This can reduce wrapped or full ranges to a usable interval and allows the
matcher to extract clamps in more cases.
Related to https://github.com/llvm/llvm-project/issues/208778
