Add mute toggle to AudioStreamPlayers

[Akosmo]

Overview

• Closes Add a 'mute' button beside audio nodes on the scene tree godot-proposals#2037

This PR introduces mute toggles that can be accessed via an AudioStreamPlayer's inspector, and the scene tree.
While -80 dB (minimum volume in the inspector slider) is not really audible, the only way to truly mute audio is to either set linear volume to 0 (-INF dB, both unavailable to the editor) or muting in the bus. Adjusting the slider or muting in the bus are not desirable in every case, since one could just want to mute one or multiple players, and easily return to the previous levels.

2026-07-02.18-22-30.mp4

Limitations

• Mute only works for the Stream playback type

I'm not comfortable editing code related to the Sample playback type. A little too much. I suggest someone to try adding that. This limitation is mentioned in the documentation.

• Mute only works in the regular/local scene tree

The toggle is not available in the remote tree. There was an attempt, but wasn't working properly. Again, I suggest someone to try adding that eventually, since it could be useful.

Notes for reviewers

In general, despite a few of my small contributions in this repository (mostly related to audio), I'm not a very experienced programmer. This is my first time modifying the AudioServer. Would appreciate someone checking that.
I'm also not super experienced with the editor code. Most of it was copied from code related to the visibility button, but modified a bit so it'd make sense.

I've tested the changes, and things seem to work on my end.

If a new button in the scene tree really is too much, I could make an alternative PR that just adds the mute property to AudioStreamPlayers, but then the proposal wouldn't be closed.