Normalize Media Library image generation to editor flow

[jeffpaul]

What problem does this address?

In 0.4.0 the ability to generate images in the Media Library and within the post editor were added. However the post-generate flows slightly differ so this issue will hopefully bring those a bit closer.

Post-generation in the post editor:

Post-generation in the Media Library:

What is your proposed solution?

• in Media Library, update the Regenerate button to Generate Another Image
• in Media Library, add Edit Prompt option to go back and edit the prompt to try image generation again
• in Media Library, update Cancel to red font and move to right aligned (away from other buttons/links)