Add identification of typescript (.ts)

[asottile]

And possibly whatever .tsx is (is it jsx? is it typescript? some sort of mashup?)

Noticed in prettier/prettier#2745

[asottile]

Seems this is already done: https://github.com/chriskuehl/identify/blob/b673286defd051c1f3c55732c314f2633ddd42d1/identify/extensions.py#L106