Add AudioComponent

[AlmasB]

This is to go to com.almasb.fxgl.dsl.components package.

It can play music or sound by considering the position of entity to which the component is attached and where the viewport is.

To address this issue, first a discussion is needed around potential use cases and how the component is to be used. A possible use case is some background audio which is played (with varying volume) only if the entity is in the viewport, as well as some sound effects that are positional.