Enhanced partition experiment.

Enhanced partition experiment.

This patch relates to motion artifacts as described in Issue 73484098

The aim of this patch is to promote the use of smaller partition
sizes in places where some of the sub blocks have very low
spatial complexity and some have much higher complexity.
The patch can have a small impact on encode speed, but much
less than alternative approaches such as lowering the rd thresholds
that limit the partition search when distortion is low.

The patch also applies a similar sub block strategy for AQ1.

Metrics results for our standard sets over typical YT rates.
(Overall PSNR, SSIM, PSNR HVS) % -ve better.

Low Res -0.274, -0.303, -0.330
Mid Res 0.001, - 0.128, -0.100
Hd Res -0.236, -0.371, -0.349
N 2K -0.663, -0.798, -0.708
N 4K -0.488, -0.588, -0.517

Change-Id: Ice1fc977c1d29fd5e401f9c7c8e8ff7a5f410717