[GuardWidening] Tighten the interface of the RangeCheck struct; NFC

Make `GuardWideningImpl::RangeCheck` into a class and add accessors.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@270611 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed