Improve TypeScript for v5.0.0

[eXamadeus]

See #480 for more context and initial PR

Upgrade Types to Support TypeScript 4.1+ Capabilities

In version v5.0.0, reselect can take advantage of some of the interesting new features of TypeScript. Using 4.1+ we can accomplish these goals:

Goals

• eliminate the need for N-valued type overloads
• fully and safely type variadic (non-array) createSelector calls
• support more than 12 selectors in variadic createSelector calls
• fix bugs w/ typings (As of TypeScript 3.1.1, types erroneously fall back to arity-agnostic createSelector signature when used with arrays #420, [TypeScript] defaultMemoize errors #384 are some examples)
• support TypeScript 3.9+ and validate it in CI

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Some caveats

• Version 5.0.0 proposal #401 proposes interesting changes to the API, we should make sure to not conflict with these changes
• ci: replace TravisCI with GitHub Actions #483 replaces the CI pipeline with GitHub Actions. We need to support testing multiple versions of TypeScript with that new CI structure (this is already worked out in refactor(typescript): upgrade to TS 4.1, simplify and generalize types #480)

[markerikson]

Based on the changes I've made in #486 and locally, I actually see most of this as being doable in a 4.x release, and in fact I've pulled them in already. It does require bumping our TS minimum to 4.2+, but frankly I consider changing TS version targets to not require a major release.

[eXamadeus]

This has been completed! Released in 4.1.0