[V3 Mod] Use a composite class for mod (#2501)

* [V3 Mod] Use a composite class for mod

This turns mod.py into acomposite class

I've split things in this up based on purpose, including `movetocore`

`movetocore` is a set of things which likely belong in the core bot and
not relying on mod being loaded.

This is part of #2500

Per discussion in discord, this should be the first thing in #2500
merged

* Move this back,
mod was importable,
and this was intended as non-breaking

* Prevent fix from being lost if merged before this.

see Cog-Creators/Red-DiscordBot#2510

* Move case creation to before sending

see #2515

* fix failed merge done in web

redbot/cogs/mod/abc.py

@@ -0,0 +1,33 @@
+from abc import ABC, abstractmethod
+from typing import List, Tuple
+
+import discord
+from redbot.core import Config
+from redbot.core.bot import Red
+
+
+class MixinMeta(ABC):
+    """
+    Metaclass for well behaved type hint detection with composite class.
+
+    Basically, to keep developers sane when not all attributes are defined in each mixin.
+    """
+
+    def __init__(self, *_args):
+        self.settings: Config
+        self.bot: Red
+        self.cache: dict
+        self.ban_queue: List[Tuple[int, int]]
+        self.unban_queue: List[Tuple[int, int]]
+
+    @classmethod
+    @abstractmethod
+    async def get_audit_entry_info(
+        cls, guild: discord.Guild, action: discord.AuditLogAction, target
+    ):
+        raise NotImplementedError()
+
+    @staticmethod
+    @abstractmethod
+    async def get_audit_log_entry(guild: discord.Guild, action: discord.AuditLogAction, target):
+        raise NotImplementedError()