Split `event_auth.check` into two parts (#10940)

Broadly, the existing `event_auth.check` function has two parts:
 * a validation section: checks that the event isn't too big, that it has the rught signatures, etc. 
   This bit is independent of the rest of the state in the room, and so need only be done once 
   for each event.
 * an auth section: ensures that the event is allowed, given the rest of the state in the room.
   This gets done multiple times, against various sets of room state, because it forms part of
   the state res algorithm.

Currently, this is implemented with `do_sig_check` and `do_size_check` parameters, but I think
that makes everything hard to follow. Instead, we split the function in two and call each part
separately where it is needed.

1 files changed, 1 insertions, 0 deletions

diff --git a/changelog.d/10940.misc b/changelog.d/10940.misc
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index 0000000000..9a765435db
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+Clean up some of the federation event authentication code for clarity.