Math.atan2(y, x) -> angle

Do not trigger current-item-changed on StandardListView if current-item is set on the same value (#5958)

Fixes #5848

This reverts commit f5d003d1.

We decided to postpone this change until a later release, in maybe a
different shape.

API Review: Remove SharedImageBuffer from public API and rename Window::grab_window() to take_snapshot()

Use SharedPixelBuffer as return value for take_snapshot() and provide counter-parts to from_rgb* in Image as to_rgb*

When stopping a timer, the removal from the timer list requires a mutable borrow.
If during that borrow the timer's closure is dropped and a `Drop` impl starts another time, then the attempt of
acquiring a mutable borrow for the timers list to insert the new timer fails.

This change exposes functionality of already existing internal API
that all renderers use to obtain pixels for upload to the screen - so
it's rather well tested.

This also exposes the `SharedImageBuffer` API, an enum that represents
different SharedPixelBuffer encodings.

This makes it possible to use component libraries with C++.

Base the commercial license on the Royalty-free license adding clauses pertaining to the fees.

Add clarification that Application may not expose Slint APIs.

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Co-authored-by: Simon Hausmann <simon.hausmann@slint.dev>

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Co-authored-by: Simon Hausmann <simon.hausmann@slint.dev>