File Block: Change the button to a Button Block

[scruffian]

Is your feature request related to a problem? Please describe.
The File Block has its own implementation of a button.

Describe the solution you'd like
The File Block should use the button Block so that the button can have the same controls as other buttons.

[rodrigo-arias]

This would be a nice improvement, currently if you select the option "Open in a new tab" for the text link, you have no way to select the same for the download button.

[glendaviesnz]

Had a quick look at this, but because it will require converting the block to use innerBlocks, it will currently suffer from the same issue as noted here in the Quote block conversion to innerBlocks PR, so probably best to leave until @dmsnell works through that.

[scruffian]

I think the best way forward here is to use an "element button": #40260

[scruffian]

This was closed by #40260