feat: Add missing Sound features .seek(), .duration, & getTotalPlaybackDuration()

[eonarheim]

===:clipboard: PR Checklist :clipboard:===

• 📌 issue exists in github for these changes
• 🔬 existing tests still pass
• 🙈 code conforms to the style guide
• 📐 new tests written and passing / old tests updated with new scenario(s)
• 📄 changelog entry added (or not needed)

==================

This PR adds the ability to ex.Sound.seek() to a specific position in the sound, it also adds the ex.Sound.getTotalPlaybackDuration() so you may know how long in seconds the sound file is. Lastly ex.Sound.duration if set will limit the duration of the clip from where played();

In order to accomplish this, ex.Sound() was refactored using a small ex.StateMachine implementation

Example

const machine = ex.StateMachine.create({
  start: 'STOPPED',
  states: {
    PLAYING: {
      onEnter: () => {
        console.log("playing");
      },
      transitions: ['STOPPED', 'PAUSED']
    },
    STOPPED: {
      onEnter: () => {
        console.log("stopped");
      },
      transitions: ['PLAYING']
    },
    PAUSED: {
      onEnter: () => {
        console.log("paused")
      },
      transitions: ['PLAYING', 'STOPPED']
    }
  }
});

Changes:

• Adds ex.Sound.seek()
• Adds ex.Sound.duration
• Adds ex.Sound.getTotalPlaybackDuration()
• Adds new ex.StateMachine()