Improve signature detection


Improve signature detection

Previously, there were a couple of hacks in play.
It was also not picking up ~~~ (signature without timestamp)
And it relied an a nasty regular expression which, although
based on Parser, may some day get out of date.
And it relied heavily on a specific signature format, which
isn't guaranteed (it's an i18n msg)

This patch changes the approach: it will use a very simple
regex to match links, and will send those through Parser to
generate the signature anew. My reasoning is that that should
be exactly the same as what Echo just received (should've
also gone through parser)

Biggest discomfort of this approach is that it's much stricter.
It should still match whatever it generated from a ~~~ or ~~~~,
but no longer the e.g. not-real signatures we were doing in
our tests. Also had to update our tests, because signatures
change depending on anon. So I had to generate all the users.
And fix some of the signature formats used in the tests.

Bug: T75426
Bug: T87852
Bug: T75366
Bug: T78424
Change-Id: Ibeff36397129fdd5d376f3668a23a45f9a014525