Eyebrow parameters should be assignable in EyeLinearDriver

[hazre]

Is your feature request related to a problem? Please describe.

After the recent SteamLink intergration update, some few eye and face tracking parameters were added to the eye manager and the avatar expressions component to fully take advantage of Quest Pro's eye and face tracking capabilities. One of these was eye brow expressions. To be exact, InnerBrowVertical & OuterBrowVertical.

But so far, I have not found a way to assign blendshapes to these parameters below, besides manually driving them.

Describe the solution you'd like

I would like to be able to assign blendshapes for InnerBrowVertical & OuterBrowVertical inside EyeLinearDriver component, similar to other eye related parameters:

Describe alternatives you've considered

Manually driving avatar's blendshapes from Eye Manager's RawOutput parameters.

Additional Context

No response

Requesters

@hazre @gourry @natbard

[shiftyscales]

Seeking input from @Frooxius.

[hazre]

I want to add something else to this. it looks like the parameters for BROW_LOWERER_R and BROW_LOWERER_L are "missing" too (they are called brow down sometimes)

I understand that Froox went for a more generic way of handling it, using a -1 to 1 range to cover both lowering and raising. But it's worth noting that basically all face tracking avatars with support for Quest Pro's brow tracking typically have this as a separate blendshape. This implementation combines the lowering and raising into a single parameter for each brow section, which is different from how many other systems handle it.

Would be nice to have two helper fields for BrowLower for each eye under EyeLinearDriver component, so users don't have to add extra logic to their avatars to be able to map it correctly to their avatar's blendshapes.