The idea is: RGBMatrix innerSpeed differs from "normal" speed.
The "normal" speed is the "outer" speed.
The innerSpeed is the speed of each step.

Same for Chaser:
The innerSpeed is the speed for each step (in Common speed mode)
Other alternateSpeeds are available for Chaser,
these are the speeds of each individual step (in Per Step mode)

The alternateSpeed allows getting/setting these new Speeds.
This will allow the VCSpeedDial to change the speed steps of a Chaser.

The main goal of alternate speeds is: when changing the "normal" speed
of a chaser or rgbmatrix, the inner speed is not affected.

Otherwise the cuelist looks stopped while playing with a speeddial

Overridespeeds are ignored anyway

Without this, when adding a sequence-container scene to a vcspeedial,
the contained sequence and it alternatespeeds
are not selectable anymore.