MNT: dock area

[GuillaumeFavelier]

This small PR allows setting dock areas other than 'left' and 'right' (namely 'top' and 'bottom').

Here is a small code snippet to try:

Details

from mne.viz.backends.renderer import _get_renderer

renderer = _get_renderer()
for area in ['top', 'bottom', 'left', 'right']:
    renderer._dock_initialize(area=area)  # <---- new parameter here
    renderer._dock_add_button(area, lambda x: None)
renderer.show()

It's a part of #10565

[larsoner]

Thanks @GuillaumeFavelier !