Hide "Sticky" position option when not available

[getdave]

If a Group block is a child of a Template Part then making it Sticky will have no effect (for explanation see #47043).

Therefore we should hide the option from any Group blocks that are children of Template Parts.

[noisysocks]

Ran into this while creating a block theme. I tried to make the Group within my header template part sticky and assumed that the feature was completely broken.

Kapture.2024-06-04.at.13.42.55.mp4

@andrewserong what do you think of Dave's suggestion? I think we need to do something until #50617 can be fixed since it's really misleading right now.

[andrewserong]

That's actually not a bad idea! I'm a bit cautious about hiding things that have been available for a long time, and there are good use cases for nested sticky positioning, but I agree that hiding it when the Group block is a child of a template part is probably a good way to go. I suspect most use cases for sticky are either at the root of the template, or within nested content rather than nested within template parts. (I.e. patterns like sticky scrolling headers are typically part of the content of a document, rather than within a header or footer).

If we do go with hiding, I'd go with an approach where we hide if there isn't yet a sticky value set. It's important that if folks move a sticky group block to another part of a template or template part, they're still about to switch the value to off.

[richtabor]

If we do go with hiding, I'd go with an approach where we hide if there isn't yet a sticky value set. It's important that if folks move a sticky group block to another part of a template or template part, they're still about to switch the value to off.

Agreed.