Add possibility to reset blocks when they are locked

[kraftner]

What problem does this address?

When a block is locked (either as part of a template or just the single block) for some (e.g. image, video) there is no way to reset them to the initial empty state.

For fully editable block content this is no problem - just delete the block.

But if you e.g. have a custom post type with a fixed template like this:

you can "reset" core/heading and core/paragraph by just deleting the text.
But for core/image and core/video you can only change them to another image/video but never go back to empty.

What is your proposed solution?

Add a button to reset the block to the initial/default state.

This could be a top level block next to "Replace":

Or inside the replace flow:

Worth considering is also if that option should always exist, or just in the case of a locked block.