AV1Enc: Fixing VBR quality issue

CTS test uncovered quality issue in case of rapid content change in VBR
mode. Because of libaom VBR resulted in >20% BR increase on some files,
we are using AOM CBR (for MediaCodec VBR) with the following restrictions:
1. Buffer control variables are set to default (for VBR)
2. MaxQP is set to 52. This will also allow to maintain quality floor

Test: atest DecodeEditEncodeTest
Bug: b/279671663
Change-Id: Ie9f2fbbc09c44104759fdef30d90c5009abbc0fe