Use separate stride for V plane in convertYUV420Planar8ToYV12

The code assumes that U and V planes in C2GraphicsBuffer will
always have the same stride (which may or may not be the case).

Pass in separate V stride and use that for populating the V plane.

Bug: 260137064
Test: atest CtsMediaCodecTestCases CtsMediaDecoderTestCases CtsMediaPlayerTestCases
Change-Id: I4ca67104e69e04aba92eb01d40b24d0af80609ab