[WIP] Stream-parsing support for file uploads

Implements stream-parsing support for incoming requests in order to save memory when handling file uploads.

Todo:
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- [x] Testing of the stream parsing support
- [x] Potential refactoring of the content-support to remove dependency on Mime/Mail components (and potentially re-use logic from stream-parsing)
- [x] Create override for `UploadFile` validator. This validator uses `is_uploaded_file()` when it encounters `UPLOAD_ERR_OK` to validate that the filename was handled via uploads, and was not spoofed. Unfortunately, this breaks for PATCH and PUT file uploads, as they are not handled natively by PHP.
- [x] Create override for `RenameUpload` filter. It uses `move_uploaded_file()`, which uses the same logic as `is_uploaded_file()`, which causes the same problems as noted above.