Enhance channel masks conversion between AIDL and legacy

Provide conversion for layouts not listed in
AudioChannelLayout::LAYOUT_* constants. In this case
the conversion is performed on bit-by-bit correspondence
between AudioChannelLayout::CHANNEL_* constants and
legacy channel bits.

Bug: 198812639
Bug: 204362366
Test: atest audio_aidl_conversion_tests
Test: atest CtsMediaTestCases:AudioTrackTest#testDownmix
Change-Id: Ie4b56350479032e31e48a8c0a5b4cc6e88416511