Add Flex Layout documentation

[HerbertsVaadin]

Solves
#2124

[github-actions]

AI Language Review

In the review of the provided files, there are no changes or issues that require improvement related to edited lines or sections. The modifications from the old files to the new ones seem to address the additions correctly, and the AsciiDoc files are appropriately descriptive, maintaining clarity and consistency.

Thus, no specific comments or corrections are needed on the revised parts.

[rolfsmeds]

We're actually trying to get away from the need for FlexLayout entirely, so I'm not sure we want to now start promoting it like this. HL now has native support for wrapping, so the only feature it has that HL and VL lacks is setDirection.

[HerbertsVaadin]

We're actually trying to get away from the need for FlexLayout entirely, so I'm not sure we want to now start promoting it like this. HL now has native support for wrapping, so the only feature it has that HL and VL lacks is setDirection.

@rolfsmeds I guess for HL and VL it would only make sense to have "reverse" direct changes, but a use case where you'd want to switch between HL and VL isn't covered I guess.

Wondering if it would be useful to add a disclamer on top, that the user should prefer to use HL or VL instead of this component, unless they have some specific scenario where the direction change is necessary?
Just brainstorming, that "Flex" is more recognizable than "horizontal layout" or "vertical layout" for outside people, so a page for it could funnel the user to the right component?

Since its not a deprecated component, feels like it should be documented.

[rolfsmeds]

Even for scenarios where direction change is needed, I think it makes more sense to use utility classes or just plain css with a div (or one of the layouts, since those are also really just flexboxen), since you typically want to change other properties as well (e.g. justification and alignment) when you change orientation.

We could also consider including FlexLayout on the HTML Elements page, as it's really just a div with some inline css.

[HerbertsVaadin]

@rolfsmeds
Sure, HTML Elements page makes sense, I can rework this PR into that.
I could write up a much smaller summary, as a separate section that page, similar to how HTML Container has a separate section. Or should it be only only a table entry?

[rolfsmeds]

I think a separate section like for the Html class would make sense.