Fix sorted_vector PMR test cases (#1207)
Fix sorted_vector PMR test cases (#1207)

Summary:
`folly::detail::std_pmr` uses either `std::pmr` or `std::experimental::pmr`.

"Polymorphic Memory Resources" has been standardized in C++17, but `pmr::resource_adaptor` was [left behind](https://github.com/cplusplus/papers/issues/33), which means `resource_adaptor` is not available when a C++17 ready standard library is detected by folly.

This commit reimplements `test_resource` without using the non-standard adaptor.

```
folly/test/sorted_vector_test.cpp:862:31: error: ‘folly::detail::std_pmr::resource_adaptor’ has not been declared
  862 | using folly::detail::std_pmr::resource_adaptor;
      |                               ^~~~~~~~~~~~~~~~
```
Pull Request resolved: https://github.com/facebook/folly/pull/1207

Reviewed By: nbronson

Differential Revision: D17003049

Pulled By: yfeldblum

fbshipit-source-id: 7bcd5b4bb4368366cd57d89b9ef88deaaff808d6

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly