[mdoc] New make test for the --dropns functionality
[mdoc] New make test, reproduces issue with --dropns when run with a secondary assembly that doesn't drop the specified namespace
[mdoc] added -dropns-assemblies parameter.
Will now only replace the namespace when the type or member is in a listed assembly
[mdoc] Formatting feedback from pull #1273
[mdoc] consolidated dropns and dropns-assemblies into a single parameter.

Based on pull request feedback, this is a simpler usage, and meets our required use-case. A sample version of this parameter would be: `--dropns MyUnifiedAssembly=MyDroppedPrefix`
Merge pull request #1273 from joelmartinez/docs-unified-fix

bugfix for mdoc update with --dropns feature