Use TSX parser instead of Typescript parser for JavaScript and JSX

[maxbrunsfeld]

JavaScript (and .jsx) files can contain JSX (and cannot use TypeScript's type assertion syntax), so we need to use the TSX dialect of TypeScript when parsing and analyzing them.

[maxbrunsfeld]

Is there any testing that should be added for this? Previously, we would have gotten parse errors on any .js files that used JSX, so maybe just a unit test that we can parse a .js file with some JSX in it?

[tclem]

Let's do something like this, but with a .jsx extension. You can use script/generate-example to help bootstrap the expected output.

[maxbrunsfeld]

While we were here, @rewinfrey and I also added some limited support for Type arguments in TSX (microsoft/TypeScript#22415).

[maxbrunsfeld]

JsxOpeningElement terms now have an optional TypeArguments child. We based this off the way that type arguments are handled in the New node.

[tclem]

LGTM. Can we do a manually run of the parse-examples target (we use to do this in CI, but travis can't quiet keep up with the workload)?