Breaking changes:

• Closes Refactor Filters #2178

Also fixes #2281 (the problem was that we had duplicate docs in filters.)

Checklist for PRs

• Added .. versionadded:: version, .. versionchanged:: version or .. deprecated:: version to the docstrings for user facing changes (for methods/class descriptions, arguments and attributes) How do we want to document this breaking change? Just a .. versionchanged:: on top of the filters module?
• Created new or adapted existing unit tests

Notable changes:

• Converted __new__ in BaseFilter to __init__ see: Overhaul of Filters #2759 (comment)

• Made _UpdateType public, so users can now do: filters.UpdateType.MESSAGES.

• deleted ChatType's filter() as discussed offline (reasoning was that Filters.chat_type was always True) .

• All _ChatUserBaseFilter subclasses have a CAPS shortcut with allow_empty=True, we can discuss to remove this / keep it default (False). This allows a user to do something like filters.SENDER_CHAT work for both Channels and Supergroups.

  Edit: It was decided that those shortcuts won't inherit from _CUBF and instead be their own, see
  https://t.me/pythontelegrambotdev/261 for discussion.

• Use a functools.partial() in DICE filter to simplify it for the user. See the examples section in Dice docs.
  Reverted. See: Overhaul of Filters #2759 (comment)

Minor changes:

• remove the name argument in _Dice (to reduce repetition, it is now built from the emoji itself)
• changed import of User, Chat in filters to TG{User, Chat} to avoid namespace conflicts.
• The filters docs are now arranged according to how it appears in source.
• Converted Optional[str] -> str in MimeType and Category (it was just plain wrong).
• Rearrange filters in the source (right now they're all over the place). Should be done after a approving review since the diff is already messy.