This introduces new `Tooltip` and `Popup` structs that unify and extend
the old popups and tooltips.
`Popup` handles the positioning and optionally stores state on whether
the popup is open (for click based popups like `ComboBox`, menus,
context menus).
`Tooltip` is based on `Popup` and handles state of whether the tooltip
should be shown (which turns out to be quite complex to handles all the
edge cases).
Both `Popup` and `Tooltip` can easily be constructed from a `Response`
and then customized via builder methods.
This also introduces `PositionAlign`, for aligning something outside of
a `Rect` (in contrast to `Align2` for aligning inside a `Rect`). But I
don't like the name, any suggestions? Inspired by [mui's tooltip
positioning](https://mui.com/material-ui/react-tooltip/#positioned-tooltips).
* Part of #4607
* [x] I have followed the instructions in the PR template
TODOs:
- [x] Automatic tooltip positioning based on available space
- [x] Review / fix / remove all code TODOs
- [x] ~Update the helper fns on `Response` to be consistent in naming
and parameters (Some use tooltip, some hover_ui, some take &self, some
take self)~ actually, I think the naming and parameter make sense on
second thought
- [x] Make sure all old code is marked deprecated
For discussion during review:
- the following check in `show_tooltip_for` still necessary?:
```rust
let is_touch_screen = ctx.input(|i| i.any_touches());
let allow_placing_below = !is_touch_screen; // There is a finger below. TODO: Needed?
```
a8e98d3f9b
