AudioMetadata: improve metadata bytestream parsing

1) simplify adding new types by automatically
   deducing the correct bytestream decoding method.
2) check bytestream length for all members.
3) update automatic parceling of simple structs
   a) allow empty structs
   b) compile time failure if number of members > 4.

Test: atest metadata_tests
Change-Id: Ia0e2f0ddb577e6f07026ab4ed736c2b52d9f6d2b
1 file changed