Build enhancement - convert from flow to typescript

[sjd78]

Convert from flow to typescript.

Flow is no longer integrated with the dev server or production build. It is 100% manual now. Either yarn flow or an your favorite ide with a flow integration will report type error. Type errors are ignored in the build.

This will give us better typing support in builds and tooling. Also, gives us the option to drop react PropTypes in favor of normal typescript typing. Patternfly-react has been doing this for awhile now.

There are a number of ways to automatically convert flow to typescript. For an example and some additional rationale: https://skovhus.github.io/blog/flow-to-typescript-migration/

Originally posted by @sjd78 in #1359 (comment)