feature: rewrite markup out of pipeline to ensure all block div's contain appropriate paragraph tags

Description

This change adds paragraph tags to block divs during decoration to avoid situations where the DOM lacks consistency depending on exactly how the block was authored.

Related Issue

Fix #44

Motivation and Context

Ideally this type of change could be made to HTML pipeline, but we can't do that for backwards compatibility reasons. By doing this here, we can slowly phase out projects that may be backwards incompatible with this type of change, and eventually (maybe?) remove it from here and add it to the pipeline.

This is likely not the only change that will eventually go into this category, which is why I did this in a new pipeline-utils file.

How Has This Been Tested?

Added test coverage. I have used similar code on projects as well

Screenshots (if appropriate):

n/a

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[x] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

[x] I have signed the Adobe Open Source CLA.
[x] My code follows the code style of this project.
[ ] My change requires a change to the documentation.
[ ] I have updated the documentation accordingly.
[x] I have read the CONTRIBUTING document.
[x] I have added tests to cover my changes.
[x] All new and existing tests passed.

adobe / aem-lib