Implemented textinput event on web platform

This is a dummy implementation of the textinput event for the web platform.

It doesn't implement anything related to `text_input_start`, `text_input_stop` or `text_input_rect` but is still dispatching a text event.

It's probably not a solution for snow but makes luxe workable with text events for the web. There seems to have 3 types of text events: `unkown`, `edit` and `input`; My PR handles only the `input` type as i'm not sure if luxe even makes use of the `edit` type.

It's a workaround, but it works.

As a side note: I'm catching only one letter per frame, i'm not sure how it's implemented on the native side or if the event loop is independant of the rest of the world but it could be an issue for more UI-oriented apps with low framerates.