WebmWriter:read kKeyBitsPerSample from input

kKeyBitsPerSample information from input was not passed to
audioTrackEntry while remuxing. Hence, the metadata of input file and
muxed file didn't match.  Now kKeyBitsPerSample is passed as it is in
the input to muxed file.

Bug: 131842669

Test: cts-tradefed run cts-dev -m CtsMediaTestCases --compatibility:module-arg
      CtsMediaTestCases:include-annotation:android.platform.test.annotations.RequiresDevice

Change-Id: I04ab296c39596d02c3f2cd9e219d8d80fe2f9185