Describe the new feature or enhancement

I think plotting eyegaze data as a heatmap can be more intuitive than a timeseries plot. Having a function in MNE for this could be nice. Maybe we could add an eyetracking module to mne.viz for this?

Describe your proposed implementation

Ultimately, It would be great if this function could be called from either a Raw or Epochs object, (and for Raw, there could be start and duration parameters), but as a start we could just implement the function to take an Epochs object.

I have some scratch code for this, but it could be improved before merging into mne. For example maybe we could implement some gaussian smoothing to make the heatmap traces look nicer.

Here's a really simple example from a short saccadic pursuit tasK:

Describe possible alternatives

Open to ideas!

Additional context

Adding this function is one of the tasks I listed in my GSoC proposal.