Adjust extended OD limits for mania difficulty change mod to reflect HR and EZ values

[dnfd1]

Resolves #35186

This change sets the OD bindable in ModDifficultyAdjust to virtual and the mania specific difficulty adjust mod is changed to override the bindable and set extended OD limits to their EZ minimum and HR maximum.

[bdach]

Not much in way of source to look at here, but I don't foresee merging this on my own without a second check with @ppy/team-client that nobody has major ideological oppositions to entertaining this type of change.

[bdach]

An inline comment describing where these specific values come from is probably warranted.

[dnfd1]

Have added a comment explaining it even though I rounded the values, since I figure it's probably useful to know why the limits are even being overriden in the first place

[smoogipoo]

Negative OD looks very wrong.

[bdach]

It does, but you actually can get into "negative OD" territory when applying Easy mod because of how special mania Easy / Hard Rock are. See #34227.

(And again, we're kinda already there elsewhere - osu! Difficulty Adjust permits negative AR already...)

[smoogipoo]

Please use round numbers. 13.61 is meaningless.

[bdach]

It's actually not that meaningless. -14.93 is what the "effective" OD is when EZ is applied to a beatmap with baseline OD 0, and 13.61 is what the "effective" OD is when HR is applied to a beatmap with baseline OD 10. (Which is why I asked for inline comments explaining what these magic numbers are.)

Whether this should be exposed to people as an option is the debate I'm interested in, but do note we're kind of already halfway there given #34227 is a thing.

[smoogipoo]

I meant the above comment from the user's perspective.

In other words, round it to -15/+15?

[bdach]

no real objections left from me, not sure about everyone else

[smoogipoo]

I suppose this is fine from me too