Provide a to_dict method

[busunkim96]

I think to_dict would be a clone of to_json that calls MessageToDict instead of MessageToJson.

proto-plus-python/proto/message.py

Lines 331 to 348 in cd9003c

	def to_json(cls, instance, *, use_integers_for_enums=True) -> str:
	"""Given a message instance, serialize it to json
	Args:
	instance: An instance of this message type, or something
	compatible (accepted by the type's constructor).
	use_integers_for_enums (Optional(bool)): An option that determines whether enum
	values should be represented by strings (False) or integers (True).
	Default is True.
	Returns:
	str: The json string representation of the protocol buffer.
	"""
	return MessageToJson(
	cls.pb(instance),
	use_integers_for_enums=use_integers_for_enums,
	including_default_value_fields=True,
	)

Currently if you want to turn an existing message into a dict you have to go through JSON. Prompted by discussion in googleapis/python-memcache#19.

import json

from google.cloud import memcache

# to json
instance = memcache.Instance(name="projects/project/locations/location/instances/instance")
instance_json = memcache.Instance.to_json(instance)
# to dict
instance_dict = json.loads(instance_json)

[software-dov]

It should be trivial to do. Is there a rough priority?

[busunkim96]

@software-dov This is not blocking anyone so not high priority. :) Just wanted to log it here to get your input.