[Enhancement] Add ability to transform audio shortcodes to audio blocks

[nfmohit]

Description

This PR adds the ability to transform [audio] shortcodes to audio blocks, like the gallery and caption shortcodes have.

How has this been tested?

This PR has been tested by going through the following steps:

1. Using the Classic Editor, added a [audio] shortcode to the content, e.g. [audio src="https://gutenberg.local/wp-content/uploads/2018/12/snow.mp3"]
2. Using the Gutenberg editor, convert the Classic block contents to Gutenberg blocks using "Convert to Blocks".
3. Made sure that the shortcode converts to an appropriate audio block and transform contains all the existing attributes of the shortcode.

Screenshots

Types of changes

This PR follows the shortcode transformation structure of the gallery and caption blocks and implements them accordingly in the audio block.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

[draganescu]

I have tested the code and it appears to work perfect.

Created a post with the classic editor and added a paragraph and an audio shortcode. Opening the post with the block editor and converting results in the audio shortcode transformed in an audio block that preserves the settings of the audio shortcode.

[youknowriad]

This might need to be rebased for the e2e tests.

[nfmohit]

Thank you so much for the rebase @youknowriad ❤️. Sincere apologies as I couldn't make it, it was a hectic week 😞

[youknowriad]

No worries, it's fine :) Thanks for the PR and I hope to see a lot more :)

[nfmohit]

THANK YOU SO MUCH 😍