Tag: allow colorField to define color for tag

[ecarreras]

This pull request includes changes to the Field and Tag classes to add new properties and methods, as well as updates to the test suite for the Tag class to cover the new functionality.

Enhancements to Field class:

• Added a private _raw_props property and a corresponding raw_props getter to store the raw properties passed to the constructor. (src/Field.ts)

Enhancements to Tag class:

• Added a colorField getter to retrieve the colorField property from the widget properties. (src/Tag.ts)

Updates to Tag class tests:

• Added tests to ensure the colorField property is correctly set to null by default and properly parsed when provided. (src/spec/Tag.spec.ts)