Add new method to .resolve() parameters instead on init

TLObject's __init__ used to call utils.get_input_* methods and
similar to auto-cast things like User into InputPeerUser as
required. Now there's a custom .resolve() method for this purpose
with several advantages:
- Old behaviour still works, autocasts work like usual.

- A request can be constructed and later modified, before the
  autocast only occured on the constructor but now while invoking.

- This allows us to not only use the utils module but also the
  client, so it's even possible to use usernames or phone numbers
  for things that require an InputPeer. This actually assumes
  the TelegramClient subclass is being used and not the bare version
  which would fail when calling .get_input_peer().

telethon/telegram_bare_client.py

@@ -7,7 +7,7 @@ from signal import signal, SIGINT, SIGTERM, SIGABRT
 from threading import Lock
 from time import sleep
 
-from . import version
+from . import version, utils
 from .crypto import rsa
 from .errors import (
     RPCError, BrokenAuthKeyError, ServerError, FloodWaitError,
@@ -420,6 +420,9 @@ class TelegramBareClient:
         if self._background_error:
             raise self._background_error
 
+        for request in requests:
+            request.resolve(self, utils)
+
         # For logging purposes
         if len(requests) == 1:
             which = type(requests[0]).__name__