wined3d: Use context->stream_info.position_transformed instead of context->last_was_rhw in state handlers.

Use of last_was_rhw in these state handlers is, firstly, confusing to read.
The variable is actually supposed to be set for *this* draw, not the last one,
and state handlers indeed expect that, but that fact isn't obvious. Reading from
context->stream_info instead is clearer.

Secondly, since last_was_rhw is set by the STATE_VDECL handler, any other state
depending on it (including some, though not all, of the sites changed here) thus
has an implicit state handler ordering assumption. This is, needless to say,
fragile. context->stream_info is computed before state handlers, so that
dependency is a bit less fragile.