Add JSX nodes to the JS2 AST

[jacksonrayhamilton]

Continuing the discussion from here in light of my comment from here…

It would be nice if js2-mode added JSX nodes to its AST, like @felipeochoa’s rjsx-mode does. This issue proposes adding such a feature to js2-mode, most likely by migrating parsing code and classes from RJSX to JS2.

Such an extension would make JS2 capable of linting and highlighting JSX code. With these capabilities available, we can justify inheriting js-mode’s capability of automatically-detecting the presence of JSX. (These matters will be addressed in separate issues.)

Once all those features are implemented, js2-mode will behave more like a parent of js-mode. Without them, js2-mode would be less capable of handling JSX than js-mode; js2-mode would continue to rely on rjsx-mode in order to fully support JSX.

[dgutov]

At some point, adding JSX support meant doing away with supporting E4X. The latter technology seems to have very much died in the meantime, however.