Angular column placeholder

[mollykreis]

Pull Request

🤨 Rationale

Adds Angular support for column placeholders, which is part of #1538.

👩‍💻 Implementation

Add placeholder to the 5 columns that support that property.

🧪 Testing

Added unit tests

✅ Checklist

• I have updated the project documentation to reflect my changes or determined no changes are needed.

[mollykreis]

@atmgrifter00, will you buddy this PR for me?

[atmgrifter00]

Should we add an example of the usage of this in the example project?

[rajsite]

Should we add an example of the usage of this in the example project?

I don't feel strongly. Wouldn't necessarily do it for every column, maybe 1-2 if done. Whichever way just a reminder to keep it consistent across with blazor