For `focused` elements in widgets, also auto-select current text where possible

@devoncarew 

`<textarea>` and `<input type="text">` and possible some others support `select()` in addition to `focus()`, which also selects the current text in the element. Make use of that.

This is a small thing which I've added by accident while addressing a bug which didn't actually call for it, but it's still potentially useful.