Fix extended values in difficulty adjust being truncated to 10 on beatmap change

[bdach]

Closes #21539.

Regressed in a243842. It was not fine to reorder the base call :(

The failure site exposing this is here:

osu/osu.Game/Rulesets/Mods/DifficultyAdjustSettingsControl.cs

Lines 41 to 53 in e47f933

	public override Bindable<float?> Current
	{
	get => base.Current;
	set
	{
	// Intercept and extract the internal number bindable from DifficultyBindable.
	// This will provide bounds and precision specifications for the slider bar.
	difficultyBindable = (DifficultyBindable)value.GetBoundCopy();
	sliderDisplayCurrent.BindTo(difficultyBindable.CurrentNumber);
	base.Current = difficultyBindable;
	}
	}

The .GetBoundCopy() call here would cause CurrentNumber to be clamped to 10, on both sides of the bind.

Cause is similar (but not 100% exactly the same) as ppy/osu-framework#5542. All bounds that may clamp the values in the bindable need to be transferred prior to the value, to ensure clamping does not occur in the process of copying values across.

This PR uses the solution from the review comment linked above, with requisite test coverage. I won't pretend it's not ugly, but I don't know how to make it not-ugly without upending more stuff than could be considered reasonable.