[dts-lint] Support testing multiple times with different compiler options

[thw0rted]

I just created this hacky workaround to a problem that I'm not sure a lot of other users have, but I figured it was worth capturing something here.

The basic problem is that @types/node needs to behave differently depending on whether or not the consuming project includes lib-dom. I'd like to write one set of tests that runs with the option lib: ['dom'] and one without. The hacky workaround is to create a tsX.Y "version" folder, which just re-uses code and tests from another version, but has its own tsconfig file. It would be better if dts-lint supported some way of specifying multiple environments.

I don't have a specific implementation in mind. Maybe if it finds a "solution style" tsconfig.json, it would run tests once for each referenced tsconfig? Maybe dts-lint gets its own config file where I can specify an array of compiler options to change across multiple runs?