Allow "free"/unconstrained aspect ration

[septatrix]

Is your feature request related to a problem? Please describe.
When sharing slides I do not know which aspect ratio the consumer will have. A ratio like 16:9 is likely the most common but laptops are commonly 3:2 and widescreen monitors are, well, wide. Instead of them seeing black bars either on the sides or top and bottom it would be preferable to not have a fixed aspect ratio and always fill the available space

Describe the solution you'd like
Support aspectRatio: null. In this case the slides' aspect ratio would not be constrained but simply fill all available space. The author would of course need to ensure that the slides still look reasonable on other ratios.

Describe alternatives you've considered
Add minAspectRatio and maxAspectRatio which the author could set to the bounds at which they still think the slides look good. I think this is overly complicated. If this is really desired the author should either just set a fixed aspect ratio or implement a custom component which checks the window dimensions and shows a warning that slides might look weird on extreme monitors (e.g. ultra wide, or tables in portrait mode)