improve: add jsx fragment factory

[simonhaenisch]

Without the fragment factory you can't use the <> ... </> as a fragment shorthand. If it's set to Fragment instead of h.Fragment, you'd have to manually import Fragment or otherwise you'd get a "Cannot find name 'Fragment'." error. With h.Fragment, <> ... </> just works.

Thanks @WickyNilliams for the hint!

[simonhaenisch]

Need to wait for https://github.com/ionic-team/stencil/pull/2846 to be merged and published, then bump the stencil version here as well.