Add "Available since" text to all android/ headers.

Also fix a few missing/incorrect annotations.

Bug: http://b/143470841
Test: treehugger
Change-Id: I1d9ec8350df03df7d80f1cc2334eef45deec30ec
diff --git a/include/android/system_fonts.h b/include/android/system_fonts.h
index f0485a1..6fd7d2c 100644
--- a/include/android/system_fonts.h
+++ b/include/android/system_fonts.h
@@ -102,6 +102,8 @@
  *
  * Use ASystemFont_close() to close the iterator.
  *
+ * Available since API level 29.
+ *
  * \return a pointer for a newly allocated iterator, nullptr on failure.
  */
 ASystemFontIterator* _Nullable ASystemFontIterator_open() __INTRODUCED_IN(29);
@@ -109,6 +111,8 @@
 /**
  * Close an opened system font iterator, freeing any related resources.
  *
+ * Available since API level 29.
+ *
  * \param iterator a pointer of an iterator for the system fonts. Do nothing if NULL is passed.
  */
 void ASystemFontIterator_close(ASystemFontIterator* _Nullable iterator) __INTRODUCED_IN(29);
@@ -116,6 +120,8 @@
 /**
  * Move to the next system font.
  *
+ * Available since API level 29.
+ *
  * \param iterator an iterator for the system fonts. Passing NULL is not allowed.
  * \return a font. If no more font is available, returns nullptr. You need to release the returned
  *         font by ASystemFont_close when it is no longer needed.