gdkarray: Inline splice and reserve

gdkarray: Inline splice and reserve

This inlines the splice and reserver GdkArray calls. These are
typically only called from the gdk_array_(append/set_size) functions
anyway, and inlining the caller means we can constant propagate the
constant arguments in those calls. Its hard to get exact numbers, but
in fishbowl i noticed a significant decrease in the time spent in
the array code when pushing and poping states.