Refactor libavf to follow NDK guidelines

* Add __INTRODUCED_IN
* Add nullability annotations
* Clarify documentations (such as mentioning UTF-8, rephrasing, etc.)
* Rename enum and its value

Bug: b/369588412
Test: boot cuttlefish
Change-Id: I2ff69092590b2b6962f131eb866843d688a9cdb1
diff --git a/libs/libavf/libavf.map.txt b/libs/libavf/libavf.map.txt
index ecb4cc9..05a5b35 100644
--- a/libs/libavf/libavf.map.txt
+++ b/libs/libavf/libavf.map.txt
@@ -1,4 +1,4 @@
-LIBAVF {
+LIBAVF { # introduced=36
   global:
     AVirtualMachineRawConfig_create; # apex llndk
     AVirtualMachineRawConfig_destroy; # apex llndk