Handle section breaks when pasting text from other sources

[bosschaert]

Description

Convert triple dashes on a line by itself to a section break.
Also handle Word-specific section breaks when pasted from Word online or desktop Word.

Related Issue

Fixes: #209

Motivation and Context

"I would like the ability to copy Word-formatted section breaks and have DA convert them to HRs so I do not have to reformat docs coming from other sources."

How Has This Been Tested?

Tested on https://dashes--da-live--adobe.hlx.live/

Unit tests to come.

Types of changes

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

Checklist:

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

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Commits

• adac977 ✅ (latest)
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[bosschaert]

I intend to add tests for this code separately.