[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/converters.py

@@ -0,0 +1,16 @@
+from redbot.core.commands import Converter, BadArgument
+from redbot.core.i18n import Translator
+
+_ = Translator("Mod", __file__)
+
+
+class RawUserIds(Converter):
+    async def convert(self, ctx, argument):
+        # This is for the hackban command, where we receive IDs that
+        # are most likely not in the guild.
+        # As long as it's numeric and long enough, it makes a good candidate
+        # to attempt a ban on
+        if argument.isnumeric() and len(argument) >= 17:
+            return int(argument)
+
+        raise BadArgument(_("{} doesn't look like a valid user ID.").format(argument))