Slot-based horizontal alignment in HorizontalLayout

[rolfsmeds]

Describe your motivation

Creating horizontal layouts where some elements are aligned to the left, some to the center and some to the right requires a decent amount of boilerplate and can be fairly challenging to figure out, especially for Flow developers unused to html/css based layouting. Using HorizontalLayout this currently requires either creating sub-layouts for each alignment, or setting margin:auto on the correct elements.

Describe the solution you'd like

An intuitive model for horizontally aligning elements in a HorizontalLayout, based on separate slots for left, center and right aligned elements, based on two new slots in HorizontalLayout: center and end.

PoC: https://codepen.io/rsmeds/pen/dygYExp
Acceptance Criteria: vaadin/platform#5038

Describe alternatives you've considered

No response

Additional context

No response