Since AO is computed at 1/4 resolution, it is necessary to upsample
the AO buffer. Until now this was done with a bilinear tap, which is
less than ideal as it can creates jaggies at edges.
High quality upsampling can now be enabled and uses a bilateral filter.
The cost is about 2.0 ms at 250MHz on Pixel 4. ES3.1 is required.