Add __INTRODUCED_IN to NdkMediaFormat.h variables too.

Bug: https://github.com/android-ndk/ndk/issues/706
Bug: http://b/113052379
Test: builds
Change-Id: I5612b0d255f8d6a3dadffdc333adfd564073c52e
Merged-In: I5612b0d255f8d6a3dadffdc333adfd564073c52e
(cherry picked from commit 0429f4094a5fc72a2af652df2ff8c1670937a13c)
1 file changed