CPLAT-11281 Only include propTypes in DDC output

[aaronlademann-wf]

NOTE: We need to coordinate the release of these changes with updates to the logsPropError* matchers in over_react_test so that consumer tests asserting propTypes logging running in dart2js don't start to fail.

Problem

propTypes are a dev-only tool that do nothing when react_dom_with_react_dom_prod.js is utilized. That production build of react is most commonly used alongside a production deploy of Dart code compiled with dart2js.

Currently, the propTypes maps remain in the dart2js output - adding unnecessary bulk to consumer module(s).

Solution

Wrap the access to Component2.propTypes in an assert() so that they are included in JS compiled using DDC, but not dart2js.

Boy Scoutin'

• Deprecated registerComponent. This should have been deprecated when Component was - but we missed it.

[aaronlademann-wf]

Just FYI - the dev SDK travis build is failing e'where - it is unrelated to the changes in this PR.