[type-scripts-build] allow users to provide names of external modules

[ncphillips]

External/Peer Dependencies must be referenced by a global name.

This name is not given by the package.json of the files in question, and is therefore guessed unless explicitly set by the user.

Current Behaviour

Building a package without these values set will output a response like the following:

No name was provided for external module 'react' in options.globals – guessing 'React'

Expected Behaviour

There should be a way to map a dependency name to a global name.