* Added a new trait `MeasureNode`.
* Added new structs `ImageMeasure` and `BasicMeasure` that implement `MeasureNode`.
* Add a field to `CalculatedSize` called `measure` that takes a boxed `MeasureNode`.
* `upsert_leaf` uses the `measure` of `CalculatedSize` to create a `MeasureFunc` for the node.

    * Added the `TextLayoutInfo` component to `TextBundle`.
    * Added the `TextLayoutInfo` component to `Text2dBundle`.
    * Changed `TextLayoutInfo` queries to be non-optional.

…into split-text-system

* Renamed `CalculatedSize` to `IntrinsicSize`. It is now non-copy. Added a field `measure` and removed `preserve_aspect_ratio`.
* Added `measurement` module to `bevy_ui`
* Added `Measure` trait. A `Measure` is used to compute the size of an intrisically sized node.
* Added `ImageMeasure` and `FixedMeasure` `Measure` implementations.
* Changed `update_image_calculated_size_system` to use `ImageMeasure`.
* Changed `upsert_leaf` to use the `Measure` of `CalculatedSize` for the `MeasureFunc` of intrinsically sized nodes.

* Added the system (dummy atm) `measure_text_system`
* Changed the system execution order so that `measure_text_system` replaces `text_system` in the order.
`text_system` now runs after `UiSystem::Flex`.

Previously the `text_system` ran before the layout was calculated and the size of the text node was determined,
so it couldn't shape the text correctly to fit the layout, and had no way of determining if the text needed to be wrapped.
There was a hack, the system `text_constraint` that tried to determine the size of the node from the local size constraints of the node in its `Style` component.
This could not work correctly, `Val::Percent` constraints just had to be ignored as they are calcualted from size of the parent node and the `Val::Px` constraints are just a guess,
without computing the rest of the layout.
Also because the `text_system` queried for changes to the `Style` component, and not the `Node` component, it couldn't react to changes in the layout correctly.
The layout system then wouldn't recieve all the information it would need to fit the text node correctly, such as the `max-content` and `min-content` sizes.

* implemented the `measure_text_system` function.
* Added the `TextMeasure` type that implements measure.
* Added the `TextQueue` resource struct.
* Added methods to the `TextPipeline` to get min and max content sizes for the text.

changes:
* Removed `TextQueue`
* Added `min_content`, `max_content` and `ideal` fields to IntrinsicSize.
* Added `ideal_height` field to `TextMeasure`.
* Fixed text system queueing and change detection issues. `measure_text_system` only queries for modified `Text`,
`text_system` queuries for `Text` or `Node` changes.

… this PR already.

Renamed `size` field of `CalculatedSize` to `previous_size`.

* rewrote text measurefunc
* text bounds for min and max content widths are precomputed

* Removed the `previous_size` field from `CalculatedSize` and replaced it with the component `UiImageSize`. The only purpose of the `previous_size` component of `CalculatedSize` was for image size change detection. It makes much more sense to store the image size directly in its own component and it enables users to query the size of a node's image if they need to.
* Added the `UiImageSize` component to `ImageBundle`.

…into split-text-system

Co-authored-by: François <[email protected]>

Co-authored-by: François <[email protected]>

…into split-text-system