Inconsistency in Volume/Gain control ranges

Value ranges for volume knobs/sliders in various plugins and parts of lmms are all over the place.

• Most of them (e.g. track volumes) use percentages, these more or less work as expected.
• Some plugins do the dB scale mapping internally and expose dB values, ignoring the user's setting. Equalizer is a nice example.
• Some use a 0 to 1 range (e.g. BassBooster), of course those won't display dB values at all.
• The Delay (Feedback knob) and Flanger (Noise knob) effects use a 0 to 1 range with the volume knob property set (which of course expects a percentage), causing a 40 dB offset in the display.
• The mixer faders are the wildest, as they seem to use percentages in the context menu, but 0 to 1 when automated.

Although the mixer faders were addressed in #5661, it was a dirty hack. The actual value ranges of controls need to be changed in order to ever reach a reasonably consistent UX.

Start by reviewing the volume controls named in the issue, including Equalizer, BassBooster, Delay, Flanger, and the mixer faders, then read the prior workaround in #5661. Define the affected control ranges and verify that display, context-menu, and automation behavior are consistent across the examples.