Cap IntRange::Width to MaxWidth (#145356)
This commit addresses a fallout introduced by #126846.
Previously, TryGetExprRange would return an IntRange that has an active
range exceeding the maximum representable range for the expression's
underlying type. This led to clang erroneously issuing warnings about
implicit conversions losing integer precision.
This commit fixes the bug by capping IntRange::Width to MaxWidth.
rdar://149444029
