Add public ApnSetting in android.telephony.

Bug: 68208293
Test: manual

Add public ApnSetting class in android.telephony. Move APN TYPE constants out from
PhoneConstants into public ApnTypeConstants.

Design doc: https://docs.google.com/document/d/1UEYjhRGSEwwccPLs_FzFD-IeOsVq63gxmAHNtDfnzAY/edit?pli=1#

Change-Id: I74d23644a872df0abc19730285ae196b6e3e39dd
diff --git a/Android.mk b/Android.mk
index 9877557..2d74249 100644
--- a/Android.mk
+++ b/Android.mk
@@ -698,4 +698,4 @@
 include $(call first-makefiles-under,$(LOCAL_PATH))
 endif
 
-endif # ANDROID_BUILD_EMBEDDED
+endif # ANDROID_BUILD_EMBEDDED
\ No newline at end of file