Create user documentation for test harnesses

[mmalerba]

Including:

• Docs for authoring harnesses
• Docs for using harnesses
• Docs for creating new harness environments
• Guide for use with Angualar Material components
• Add thorough TSDoc and corresponding generated docs for individual harnesses

[devversion]

For reference: Related to #17063

[jelbourn]

Fixed by #17754

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