extractors: allow OEM to control output type for WAV/FLAC

Based on some usecase, outputing in float is not an option.

Should allow a property to select the behavior

Bug: 140952553
Test: NativeDecoderTest#testExtractor
Test: MediaExtractorTest#testFlacIdentity
Change-Id: Idf2bf382f50d12c00a85aa7bb5582fb0439c6ea1
Signed-off-by: Jean-Baptiste Théou <jb@essential.com>