Captions/Subtitles are affected by FPS and timescale

When closed captions/subtitles are enabled (closedcaptioning 1), there are three parts to them: The pop-in animation (where it starts a little higher than it should and drops down), the "still" part (where it's opaque and motionless as the sound plays), and the fade-out (where it slowly becomes less translucent).

- The pop-in is affected by frame rate (bad). With fpscap 300; vid_wait 0, I sometimes don't see a single frame of the pop-in on a 60Hz monitor.
- The pop-in is unaffacted by timescale (good?).

- The "still" part is unaffected by frame rate (good).
- The "still" part is partially affected by timescale (bad?). If timescale is above 1.0, the "still" part has its normal duration. If timescale is less than 1.0, the "still" part won't be longer than the sound itself, but if the subtitle normally lasts shorter than the sound (like sfx_ambmac, ID 38 in v2.2.10's sound test), it can be extended up to the length of the sound itself. (For reference, timescale doesn't affect the playback speed of sounds.)

- The fade-out is unaffected by frame rate (good).
- The fade-out is affected by timescale (may be unintentional?).