swift234

RangeReplaceableCollectionType review changes

- Clean up tests
  - Create API-specific test structures with clearer labels
  - Use `OpaqueValue`s in test collections
  - Make tests non-generic to allow array literal declarations
  - Remove some unused functions
  - Test return values for mutating functions that return a value
  - Add expect* test source locations
- Add _customRemoveLast ad-hoc default implementation for `removeLast`
- Add default implementation for reserveCapacity that does nothing.

Swift SVN r29905