Fix sliders ignoring actions past the initial hitcircle

[swoolcock]

Previously, actions would correctly trigger the initial hit circle, but were ignored when tracking the ball. This meant that the tracking ring was never displayed, and slider ticks were always counted as a miss.
The fix is to make the slider ball keep track of actions (instead of mouse buttons), and to make hit circles not consume the action if their direct parent is a slider (so that the slider ball will correctly accept the initial OnPressed).

[peppy]

The correct fix likely involves exposing PressedActions in KeyBindingInputManager and checking the pressed state of the appropriate actions.

[swoolcock]

I wasn't sure if there was a way of publicly checking the currently pressed actions, otherwise I would have done it in a similar way to the old HasMainButtonPressed.

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