Improve selection of simulcast streams

Extracted from #5535

Currently the simulcast streams are set as follows:

• If call view is in grid mode -> Medium quality
• If a participant is selected or promoted -> High quality
• Otherwise -> Low quality

However, this does not take into account the actual size of the cells in the grid, or that if a participant is selected the promoted participants will not be shown in the main view.

This could be improved, for example, with the following approach:

• If a participant is selected:
  • Selected participant -> High quality
  • Any other participant fallback to the grid quality
• If no participant is selected but a participant is promoted and the call view is in speaker mode:
  • Last promoted participant -> High quality
  • Any other participant fallback to the grid quality
• If the call view is in grid mode, or for any other participant besides the promoted and selected ones in speaker mode (they will be shown also in a grid below the main speaker):
  • Set quality based on the size of the cells of the grid

What would need to be defined (and thoroughly tested) is the threshold used for each quality and each cell size 🤷