Add Export-API.ps1 script for semi-automated API listing generation

[trrwilson]

• Intended for maintainer use in this repository
• Uses and requires the private port of GenApi tool

Our previous use of the ApiView tool is currently blocked and already presented a good opportunity to optimize.

There are gaps, however, including:

• Uninformed alphabetical ordering reorders enum values, intermixes constructors/properties/methods, etc. -- generally making things less human-readable
• Attributes like [Experimental] are no longer reflected