* Removed the `Undefined` variant from `Val`.
    * Set Val's default variant to `Auto`.
    * Updated ui examples.
    * Removed `Val::Undefined` conversion code.

    * Removed the `Undefined` variant of the `Val` enum.
    * Changed `UiRect::default()` to set all fields to `Val::Px(0.0)`.
    * Added the `Inset` type that is a copy of `UiRect` but its defaults are all
        `Val::Auto`.
    * Renamed the `position` field of `Style` to `inset` and changed its type to `Inset`.
    * Updated the UI examples to remove or replace any use of `Val::Undefined`.
    * Updated the UI examples to use `Inset`.

…-val-undefined

        Added a type `Breadth`, that is similar to `Val` but with only evaluatable variants.
        Gave UiRect a type parameter, so it can take `Breadth` or `Val` values.
        Added tests for `Breadth` and `UiRect`.
        Changed style properties to use `Breadth` instead of `Val` for the padding and border properties.
        Changed `bevy_ui::flex::convert::from_rect` to take an `UiRect<T: Into<Val>>` instead of a `UiRect`.
        Made minimal necessary changes to the examples.

…padding and border values in `bevy_ui::flex::convert::from_style`

* 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.

…-latest

…-0.3.3

… taffy-0.3.3

…y-0.3.3

* cleaned up conversion and geometry
* fixed examples

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>

…taffy-0.3.3

This reverts commit 035f0dc.

This reverts commit 6f32916.

This reverts commit e5a6144.

This reverts commit 623c287.

This reverts commit 21fd333.

This reverts commit 492bbaf.

This reverts commit 115f98c.

This reverts commit 796b2e1.

This reverts commit 33c8e91.

…nto taffy-0.3.3"

This reverts commit a513acb.

This reverts commit 2572c39.

 into taffy-0.3.3"

This reverts commit aec59ec.

This reverts commit 02679cd.

…to taffy-0.3.3"

This reverts commit 1471f3b.

* disabled Taffy's gap feature
* added `Stretch`, `Start` and `End` variants to `Style` enums where appropriate.
* Modified `from_style` and associated helper functions to work with Taffy 0.3.3

…eAuto::Points(0.)`

* Added the variant `Unset` to `AlignItems`.
* Improved the documentation for the `Style` enum properties.

… of JustifyContent.