Indicate when a block has custom padding styles applied

[richtabor]

Is your feature request related to a problem? Please describe.
With the new padding styles added to the Cover (and other blocks soon) #21492, there should be a way to programmatically indicate that a block has a custom padding style set. This way, a theme's default padding styles previously associated with these blocks can be ignored if that class is present (only applying padding with :not(.has-custom-padding) or the like).

Describe the solution you'd like
A .has-custom-padding class is added to the block, the same way other attributes are indicated (such as .has-background, .has-background-dim and other classes.

Describe alternatives you've considered
If a custom padding style is added to a block, I would have to add a class manually via the Advanced settings panel, in order to ignore a theme's pre-configured block padding. Not ideal.

Screenshot

[getsource]

Do you think the approach in #30074 makes sense, or is there a better place higher up to add the class?

[getsource]

@richtabor Do you still think it makes sense to do this, given that it's able to be controlled by block themes directly?