Fix AAC-LC Specific Config in test vectors to obey ISO+IEC-14496-1:2010 spec.

  - Resolves both parts A and B in #119 for the test vectors.
    - Part A: Add missing "expandable" size field to both of the `DecoderConfigDescriptor` and `DecoderSpecificInfo`.
    - Part B: Flip `DecoderConfigDescriptor` `reserved` bit to 1.
    - Based on AOMediaCodec/iamf-tools@57324193.

Author: jwcullen

proto/codec_config.proto

@@ -99,7 +99,7 @@ message AacDecoderConfig {
   optional uint32 object_type_indication = 1 [default = 0x40];
   optional uint32 stream_type = 2 [default = 5];
   optional bool upstream = 3 [default = false];
-  optional bool reserved = 4;
+  optional bool reserved = 4 [default = true];  // As per ISO 14496-1:2010.
   optional uint32 buffer_size_db = 5;
   optional uint32 max_bitrate = 6;
   optional uint32 average_bit_rate = 7;