Block Theme Previews: Activate button has no loading state

[scruffian]

What problem does this address?

When activating a block theme from a preview, the "Activate" button should show a loading state, but instead it just stays blue:

Screen.Recording.2023-10-11.at.16.51.40.mov

What is your proposed solution?

The activate button needs a loading state to communicate clearly to the user that an action is happening in the background. This is how the save button usually works in the site editor.

Props to @autumnfjeld for raising this.

[scruffian]

I spent a long time investigating this today. Here are my findings.:

1. The state of the button that we care about is the one in this file.
2. Setting isBusy to true on this button gives it a loading state.
3. At present this state is connected to the isSavingEntityRecord selector.
4. This selector doesn't work for activating a theme, since a theme activation isn't an entity.
5. The action that activates the theme is triggered by the save panel not the save button, which makes it very difficult to connect the two together.

I am not sure how to proceed. I think we need a way to save the state of the activation in the global state, which means we probably need a new key for it in the store.

[autumnfjeld]

Props to @autumnfjeld for raising this.

I'm just the messenger props go @fushar and also our great testers. :)

[okmttdhr]

I am not sure how to proceed. I think we need a way to save the state of the activation in the global state, which means we probably need a new key for it in the store.

@scruffian
This seems to make sense to me, as the two components are independent!

[arthur791004]

@scruffian I proposed #55658 to resolve this issue. It's simple but I'm unsure whether it's a good idea. WDYT?