MediaCodec CTS: Code refactoring

Move code that is common across media codec tests to codec test
base class

Bug: 147573846
Test: atest android.mediav2.cts.CodecEncoderTest \
android.mediav2.cts.CodecDecoderTest

Change-Id: I82850f5f2021155b2243adbd0f27532951f46a33
Merged-In: I82850f5f2021155b2243adbd0f27532951f46a33
3 files changed