Split string capacity test into two parts and mark one part as UNSUPPORTED when using sanitizers.

The test is split such that:
- max_size.pass.cpp tests that string::resize() fails to allocator for max_size
  and max_size -1
- over_max_size.pass.cpp tests that string::resize() throws a length error for
  max_size + 1

The test was split into two because max_size.pass.cpp cannot pass with 
sanitizers but over_max_size.pass.cpp can.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@221969 91177308-0d34-0410-b5e6-96231b3b80d8