WIP: TextLayout|View: Add missing (inout)s on TextIters
The lack of an annotation in such cases means Vala assumes it can pass the TextIter by value, but these methods need to update the iter, so we need Vala to pass by reference. Adding (inout) allows that to happen.
N.B.: marking as WIP because
(inout) doesn't seem ready for primetime; see ongoing discussion in #78