Fix casting issues on macOS

Summary:
`size_t` is platform-dependent, and on macOS it is defined as
`unsigned long long`. This is not the same type as is used in many calls
to templated functions that expect the same type. As a result, on macOS,
calls to `std::max` fail because a template function that takes
`uint64_t, unsigned long long` cannot be found.

To work around the issue:

* Specify explicit `std::max` and `std::min` functions where necessary,
  to work around the compiler trying (and failing) to find a suitable
  instantiation.
* For lambda return types, specify an explicit return type where necessary.
* For `operator ==()` calls, use an explicit cast where necessary.

(cherry picked from FBD15030283)