Add cell placeholders

[mollykreis]

Pull Request

🤨 Rationale

This PR adds a placeholder configuration to the following table columns as described in #1869:

• anchor
• date-text
• duration-text
• number-text
• text

This is part of #1538. The remaining work is to add the placeholder attributes to the Angular and Blazor wrappers for each column.

As part of this PR, I also included best practices established for each column in the storybook docs. These are adapted from the placeholder HLD.

👩‍💻 Implementation

I implemented this change in a similar way as #1914. Specifically, I updated TableColumnTextCellViewBase to have its own implementation of columnConfigChanged and cellRecordChanged that calls a new applyPlaceholderTextIfNeeded function. This required me to create a TableColumnTextBaseCellRecord interface to enforce that the cell records used by TableColumnTextCellViewBase have a value property and to create a TableColumnTextBaseColumnConfig interface to enforce that the column configs used by TableColumnTextCellViewBase have an optional placeholder property.

🧪 Testing

• Updated/created unit tests
• Manually tested in storybook
• Updated matrix tests to test each relevant column with & without a placeholder

✅ Checklist

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

[mollykreis]

@m-akinc, will you buddy this PR for me?