This adjusts the positioning to work more the way we want:
* Tooltip is position on the top or bottom edge of the target depending on where
space is available
* Tooltip and chevron are centered
In addition, more bits borrowed from `ContextualMenu` are not needed, so they
have been removed for simplicity.
Part of https://github.com/vector-im/riot-web/issues/9753
Part of https://github.com/vector-im/riot-web/issues/9716
As part of reactions and editing work, we're adding a new style of tooltip that
allows interacting with the content of the tooltip. `ContextualMenu` is closest
out of the things we have today, but it doesn't position in quite the way we
want and it's already quite complex.
To get started, let's first clone that to a new `InteractiveTooltip`.
Part of https://github.com/vector-im/riot-web/issues/9753
Part of https://github.com/vector-im/riot-web/issues/9716
