Show some Customizer buttons only when needed

[pavelevap]

Buttons "Randomize uploaded headers", "Randomize suggested headers" and "Reorder" (for widgets) should be visible only for more than 1 item (for header images) and more than zero item (for widgets)?

[ehg]

With regard to the Header randomize button, it is intentionally shown when there is only one image for discoverability reasons. See https://core.trac.wordpress.org/ticket/21785#comment:37

[celloexpressions]

Hide the reorder-widgets button when a widget area is empty.

[celloexpressions]

Let's keep the randomize headers button per ehg.

For widgets, I've attached a patch that hides the reorder toggle when there are no widgets. In this patch, the button is shown when there is only one widget in the sidebar, for the move-to-widget-area functionality.

[ocean90]

In 31255:

Customizer: Hide the reorder-widgets button when a widget area is empty.

props celloexpressions.
fixes #27787.