Feature: Audio keyvalues for various Portal 2 props that lack customizable sounds

[Zepalesque]

Which component should be improved?

Audio

Describe your suggestion

Some entities, like the prop_testchamber_door and the prop_button have sound effects that cannot be changed without replacing the sound file, as the sounds are hardcoded, rather than using animation events. However, making them only use animation events could break existing models that have no sounds. A good solution for this might be adding audio keyvalues for the different sound effects, like the test chamber door opening, closing, locking and unlocking, or for the pedestal button, when it is pressed or releases.

Note: Some props, like the prop_floor_button don't have this issue, as they use animation events rather than hardcoding the sounds.

[ozxybox]

@AWildErin does this relate to some of the work you were up to?

[AWildErin]

This is a dupe in of #1565. Or rather the other way around, but might as well close this since you assigned me to that one.