[pango-display-list] Use the Cogl journal for short runs of text
[pango-display-list] Use the Cogl journal for short runs of text

For small runs of text like icon labels, we can get better performance
going through the Cogl journal since text may then be batched together
with other geometry.

For larger runs of text though we still use VBOs since the cost of logging
the quads becomes too expensive, including the software transform which
isn't at all optimized at this point.  VBOs also have the further advantage
of avoiding repeated validation of vertices by the driver and repeated
mapping of data into the GPU so long as the text doesn't change.

Currently the threshold is 100 vertices/25 quads. This number was plucked
out of thin air and should be tuned later.

With this change I see ~180% fps improvment for test-text. (x61s + i965 +
Mesa 7.6-devel)

ebassi/clutter,GNOME/clutter,collects/clutter,heysion/clutter-clone,ebassi/clutter,Distrotech/clutter,heysion/clutter-clone,spatulasnout/clutter,spatulasnout/clutter,rkudiyarov/clutter_osx,ebassi/clutter,djdeath/clutter,djdeath/clutter-android,jigpu/clutter,jigpu/clutter,collects/clutter,djdeath/clutter,nobled/clutter,rkudiyarov/clutter_osx,kerrickstaley/clutter-vala,djdeath/clutter-multithreaded,nobled/clutter,dlespiau/clutter,GNOME/clutter,collects/clutter,djdeath/clutter-android,dlespiau/clutter,heysion/clutter-clone,ebassi/clutter,rkudiyarov/clutter_osx,Distrotech/clutter,Distrotech/clutter,GNOME/clutter,djdeath/clutter-multithreaded,jigpu/clutter,GNOME/clutter,GNOME/clutter,tardyp/clutter,djdeath/clutter-multithreaded,jigpu/clutter,tardyp/clutter,djdeath/clutter,nobled/clutter,djdeath/clutter-android,kerrickstaley/clutter-vala,collects/clutter,djdeath/clutter-android,spatulasnout/clutter,Distrotech/clutter,jigpu/clutter,dlespiau/clutter,spatulasnout/clutter,ebassi/clutter,djdeath/clutter-multithreaded,kerrickstaley/clutter-vala,jigpu/clutter,djdeath/clutter,spatulasnout/clutter,Distrotech/clutter,rkudiyarov/clutter_osx,djdeath/clutter,kerrickstaley/clutter-vala,collects/clutter,heysion/clutter-clone,djdeath/clutter,tardyp/clutter,Distrotech/clutter,heysion/clutter-clone,djdeath/clutter-android