fix: fix cell widths overridden by readjusted smaller breakpoints in XY Grid #10468

fix: fix cell widths overridden by readjusted smaller breakpoints in XY Grid #10468

With margin gutters, a cell width is defined with its gutter. This is why we have to readjust all sizes and not only `.cell` when applying the new gutter in a bigger breakpoint. This must include all sizes for smaller breakpoints too.

Before this commit there was an optimization that prevent gutters for smaller breakpoints without a new gutter defined to be regenerated. This can seems logical since no gutter was generated for this breakpoint so there is nothing to readjust.

However, because the gutter is defined _with the width/height_, the readjusted width/height of readjusted gutters (with a custom gutter) overrides the width/height of bigger non-readjusted (without a custom gutter) breakpoint.

Changes:
* Readjust gutters for all breakpoints even without new gutter defined
* Add explainaitions

Closes https://github.com/zurb/foundation-sites/issues/10468