Fix cyclic deps: rent_a_codec<->audio_coding and rent_a_codec<->neteq

In short, what I did was to

  * Remove acm_common_defs.h (the stuff in it was used only by
    acm_codec_database.cc).

  * Move audio_coding_module_typedefs.h to a new build target.

  * Move the NetEqDecoder enum (and the associated
    NetEqDecoderToSdpAudioFormat function) to a new file in a new
    build target.

BUG=webrtc:7243, webrtc:7244

Review-Url: https://codereview.webrtc.org/2723253005
Cr-Commit-Position: refs/heads/master@{#17005}
diff --git a/webrtc/modules/audio_coding/neteq/decoder_database.cc b/webrtc/modules/audio_coding/neteq/decoder_database.cc
index 16bec04..d147d67 100644
--- a/webrtc/modules/audio_coding/neteq/decoder_database.cc
+++ b/webrtc/modules/audio_coding/neteq/decoder_database.cc
@@ -42,8 +42,7 @@
 
 DecoderDatabase::DecoderInfo::DecoderInfo(NetEqDecoder ct,
                                           AudioDecoderFactory* factory)
-    : DecoderInfo(*acm2::RentACodec::NetEqDecoderToSdpAudioFormat(ct),
-                  factory) {}
+    : DecoderInfo(*NetEqDecoderToSdpAudioFormat(ct), factory) {}
 
 DecoderDatabase::DecoderInfo::DecoderInfo(const SdpAudioFormat& audio_format,
                                           AudioDecoder* ext_dec,
@@ -135,8 +134,7 @@
       !CodecSupported(codec_type)) {
     return kCodecNotSupported;
   }
-  const auto opt_format =
-      acm2::RentACodec::NetEqDecoderToSdpAudioFormat(codec_type);
+  const auto opt_format = NetEqDecoderToSdpAudioFormat(codec_type);
   if (!opt_format) {
     return kCodecNotSupported;
   }
@@ -175,8 +173,7 @@
     return kInvalidPointer;
   }
 
-  const auto opt_db_format =
-      acm2::RentACodec::NetEqDecoderToSdpAudioFormat(codec_type);
+  const auto opt_db_format = NetEqDecoderToSdpAudioFormat(codec_type);
   const SdpAudioFormat format = opt_db_format.value_or({"arbitrary", 0, 0});
 
   std::pair<DecoderMap::iterator, bool> ret;