Implement legacy beatmap encoding for all rulesets

[smoogipoo]

Prereqs:

• Fix beatmap encoder by enabling untested test cases #8818

Biggest changes are those to mania since hitobject samples may have changed for converts. It needs to be looked into further anyway, since I'm fairly certain it's not handled correctly anyway:

#8595
#2506

[bdach]

I read through this. A few places were a little weird (drumrolls with IHasCurve, although I do like that it was an explicit implementation, or the encoder not being able to reference LEGACY_VELOCITY_MULTIPLIER due to library separation) but after some thinking I figured this is legacy stuff anyway and doing this "properly" would probably be a headache and a half, so probably best to leave it as-is and deal with it if it ever becomes a problem (which it probably won't).

As to actual correctness of the changes I mostly defer to the tests themselves as I'm not very familiar with the osu! file format but it all looked correct as far as I could tell. History looks bad here too though, same as in the other PR.

[peppy]

can't see any issues.