Fix up hacky detection of `React.Component` and `React.ReactNode`

[grncdr]

Currently the code just stringifies types and compares them against constant strings. This doesn't work if the import isn't named React.

Investigation needed: can we do reliable symbol comparisons with ts.Symbol.equals?

Tests should cover:

• import {Component, ReactNode} from 'react' && class Foo extends Component<{n: ReactNode}> {}
• import * as R from 'react': class Foo extends R.Component<{n: R.ReactNode}>