Add layout flow to text content in media and text block

[Rishit30G]

What?

Closes: #70264

Why?

This PR is necessary to fix the text content layout issue in the media and text block

How?

Added the following classes to the text content part is-layout-flow and wp-block-media-text__content-is-layout-flow.

Testing Instructions

• Add a Media Text block
• Add some content
• Notice now there is no more extra padding on top or bottom when vertically aligning the content

Screenshots or screencast

Before	After

[Rishit30G]

Note

I was able to fix this issue for the editor, but I'm curious to know how we can fix this for the frontend, I tried working with save.js but didn't get the expected results

cc: @t-hamano

[t-hamano]

@Rishit30G Thanks for the PR!

Adding the is-layout-flow class to the inner blocks directly isn't the right approach. I think this needs to be resolved via blockGap support.

Furthermore, this PR would conflict with #67208, which means we need to decide where blockGap support should be applied first.

Let me close this PR for now.

[Rishit30G]

Makes sense @t-hamano, thanks for the review and suggestion!