gtk/{Text,Tree}Iter: derive Debug

[fengalin]

So that a struct using these types can also auto derive Debug.

Another solution could be to add a Debug impl in manual code,
but since these are iterators, there's not much we can show.

Other boxed_inline candidates in gtk-rs-core and gtk3-rs use manual Debug impl AFAICT.

[GuillaumeGomez]

I wonder if we should do the opposite and derive Debug by default unless set to false...

[fengalin]

I wonder if we should do the opposite and derive Debug by default unless set to false...

If I refer to graphen, which uses the most boxed_inlines AFAICT, it makes sense to manually implement. You would either get useless inner indirection or require to manually implement anyway to either call the C accessors or use the proper cast (see quad.rs for instance).

[GuillaumeGomez]

Good point. :)

cc @sdroege