Add MIME type for "amr" audio files.

More details here:
https://en.wikipedia.org/wiki/Adaptive_Multi-Rate_audio_codec

Bug: 143521987
Test: manual
Change-Id: Ic99672b746920d8733873e9df57a7c534e04e9d5

mime/java-res/android.mime.types

@@ -73,6 +73,7 @@
 ?audio/3gpp 3gpp 3ga
 ?audio/aac-adts aac
 ?audio/ac3 ac3 a52
+?audio/amr amr
 ?audio/imelody imy
 ?audio/midi rtttl xmf
 ?audio/mobile-xmf mxmf