applets/taskmanager: Reintroduce ability to disable audio indicator/controls

Reintroduce ability to disable audio indicator

• We previously removed it because we had assumed that it would always be useful to indicate audio playback, and instead replaced it with an option to disable it as an interactive mute button. User demand has shown this is not the case, with many people preferring a clean indicator-less aesthetic.
• This commit reintroduces an option to disable the indicator altogether, with a subordinate option to toggle its interactivity. By default, both options are enabled.
• BUG: 499891

Add option for tooltip volume controls

• This was previously also disabled by the setting that would hide audio indicators on tasks. This commit re-introduces this feature, but with a specific option.
• CCBUG: 499891

Handle tooltip media controls as with volume controls

• This commit changes the option introduced in the previous commit to also handle media controls.
• Squash me or drop me!

Give proper indent to checkbox on Behavior page

• Makes the indentation correct, matching the new indented controls introduced in this MR.

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Screenshot:

with new "Show an indicator when a task is playing audio" option, existing option made subordinate to, and new "Show media and volume controls in tooltip" option