Be explicit about error conditions in DomAction and HtmlContent processors

[jonsnyder]

Description

This updates the DomAction and HTMLContent processors to be more explicit in how to handle items that are invalid. Namely it should not mark them rendered and not include them in the display notification.

Related Issue

Motivation and Context

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change which does not add functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA or I'm an Adobe employee.
• I have made any necessary test changes and all tests pass.
• I have run the Sandbox successfully.