Set center value of W/D knob at 0

[Monospace-V]

Enhancement Summary

The W/D knob, when set to 0, should be grey on either side of the knob.

Presently, when w/d is at 0, the area between -1 and 0 is highlighted on the knob. (see image)

(ie, arc active on a knob. Should be activated beyond 0, not -1 at knob beginning.)

Other knobs which display the behaviour expected:

W/D by contrast

Justification

At 0 the w/d knob shouldn't give the impression that there is a 50% w/d mix.
The enhanced behaviour would be visually accurate.
This would also clear up some of the confusion that may have led to the opening of #6029.
Users are less likely push w/d to -1 by mistake confusing it for 0.

Implementation?

It could be convenient to implement a check that centres the highlight at zero for all knobs that contain a zero. Basically universally set the center value to zero. Is this possible?
For this case, we can just place m_wetDryModel.setCenterValue( 0 ); in Effect.cpp.

Took me an while to understand enough of the linking in this codebase to come to this, but this seems very simple. I would like to try and implement this specific fix.

Mockup

Current behaviour:

Expected behaviour:

[M4rotte]

I support this modification. I find particularly problematic having the knob at 1 when adding a Feedback delay line effect.

[DomClark]

Implemented in #7077.