Add ability to use GitHub Actions to build NVDA

[nvdaes]

Is your feature request related to a problem? Please describe.

Currently, documentation about building NVDA with AppVeyor is provided.
However, people may find easier to use GitHub Actions for testing.

Describe the solution you'd like

Add a .yml file in the root of NVDA with a workflow_dispatch event, so that it can be used manually without interfering in the workflow used by the developers, i.e., Appveyor.

Describe alternatives you've considered

Creating a workflow (.yml file) when desired, and remove it after finishing pull requests.

Additional context

Smetimes, it's difficult to test NVDA locally for any reason.

[nvdaes]

cc: @XLTechie

[seanbudd]

Closing as duplicate of #10516