[analyzer] Fix a few size-type inconsistency relating to DynamicExtent

Size-type inconsistency (signedness) causes confusion and even bugs.
For example when signed compared to unsigned the result might not
be expected. Summary of this commit:

Related APIs changes:
1. getDynamicExtent() returns signed version of extent;
2. Add getDynamicElementCountWithOffset() for offset version of element count;
3. getElementExtent() could be 0, add defensive checking for
   getDynamicElementCount(), if element is of zero-length, try
   ConstantArrayType::getSize() as element count;

Related checker changes:
1. ArrayBoundCheckerV2: add testcase for signed <-> unsigned comparison from
   type-inconsistency results by getDynamicExtent()
2. ExprInspection: use more general API to report more results

Fixes https://github.com/llvm/llvm-project/issues/64920

Reviewed By: donat.nagy, steakhal

Differential Revision: https://reviews.llvm.org/D158499