Plot function for virtual channels in bridging electrode EEG analysis

Describe the new feature or enhancement

The nice tutorial made by @alexrockhill in https://mne.tools/dev/auto_examples/preprocessing/eeg_bridging.html#sphx-glr-auto-examples-preprocessing-eeg-bridging-py shows how one can plot the "virtual" <bridge_elec1>-<bridge_elec2> signal and visually confirm if the data is in fact bridged.

I would like to have this plot as a function to enable someone's workflow.

Describe your proposed implementation

The https://mne.tools/dev/generated/mne.preprocessing.interpolate_bridged_electrodes.html#mne.preprocessing.interpolate_bridged_electrodes function internally has a method for computing the "virtual channels" for the sake of interpolation.

I would just refactor that to a private method, and then add a plot method for plot_bridged_virtual_ch to recreate this plot but for all bridged electrode pairs: https://mne.tools/dev/auto_examples/preprocessing/eeg_bridging.html#plot-the-raw-voltage-time-series-for-bridged-electrodes

Additional comments

I don't think we want to return the full Raw object probably(?), but the plot is generated from a "Raw" copy of the original data + bridged_idx. Should we plot all virtual channels? This might be cluttered because there could be MANY virtual channels...?

WDYT? @alexrockhill

Start with mne.preprocessing.interpolate_bridged_electrodes and the EEG bridging tutorial, especially the plot of raw voltage time series for bridged electrodes. Determine how the existing virtual-channel computation can support a public plot function for bridged electrode pairs; done means the function recreates that plot with an agreed behavior for multiple virtual channels.