feat: add tooltip builtin

[michneaionuc]

This PR introduces built-in tooltip support in Slint (#6446).

You can now attach a ToolTip to an element and get consistent hover behavior (including delay and placement), with proper runtime popup handling and style integration.

Highlights

• Added built-in ToolTip behavior and lowering pipeline
• Added tooltip popup kind (Tooltip) alongside existing popup kinds
• Added validation with clear compiler errors (for example: more than one tooltip on the same parent)
• Added tests for tooltip behavior and syntax errors
• Added tooltip docs in builtins.slint
• Added tooltip examples in Gallery->Controls

How to test

1. Run the Gallery example and try tooltip interactions
   cargo run -p gallery
   In the UI, open Controls and find the ToolTip section

2. Regenerate docs locally

cargo run -p slint-doc-generator -- generate-mdx
cargo run -p slint-doc-generator -- screenshots --overwrite docs/astro/src/content
pnpm -C docs/astro dev

[ogoffart]

One detail about the API is that I wonder how to have custom content, while still having themed tooltip decoration.

[ogoffart]

I would also like to see a bit more tests for the error case.
What if you have neither test nor element in it, what if you have both, what if you set the x, y property to a Tooltip. Tooltip in places that shouldn't accept tooltip (eg, Timer, Menus, other Tooltip)
At least each error message that you introduce should basically be tested.
Can you put @children in a tooltip?
Can you inherit from Tooltip?
Can you put a Tooltip in a layout?
And all other corner case you can think off.

There should be either syntax test or test that this works.

[Murmele]

@michneaionuc I don't see any tooltip when using qt as backend only for winit

[Murmele]

I used the tooltip_on_button.slint example
Is it possible to change the distance of the tooltip to the button?

[michneaionuc]

@michneaionuc I don't see any tooltip when using qt as backend only for winit

I'm gonna have a look at it. Thanks

[michneaionuc]

I used the tooltip_on_button.slint example Is it possible to change the distance of the tooltip to the button?

Not currently, but good point, I think we should add a configurable tooltip offset property