Block Library: Column: Add draggable resize control

[aduth]

Previously: #15499

As of #15499, it is possible to resize a Column block using the "Percentage width" input in the block inspector. We should seek to enhance this by adding optional interactive controls within the rendered display of the block itself.

Implementation specifics:

It should likely be implemented using ResizableBox, and behave similarly to the Media & Text block resizing.

I had originally spent some time on this in #15499, reflected in the following in-progress (including clumsy attempts at math) diff at: https://gist.github.com/aduth/dc2136eb703a3c1dad39b3879f37ac6e

Per @jasmussen's comment at #15499 (comment), this may need to be reconsidered, however. The above diff assumes that each column would display its own resizer, and only when it is selected. From this design recommendation, the resizer may well become either part of the rendered output of the Columns parent block, or as some customization of how it renders InnerBlocks. It may be necessary to enhance InnerBlocks to customize the rendered output of individual blocks in the nested area, similar to what was done for customizing appender behavior with renderAppender introduced in #14241 (e.g. renderBlock).

[paaljoachim]

I am wondering if we can close this issue?

@gziolo

[gziolo]

I don't know, it seems like a valid feature request.

[paaljoachim]

I agree.