Address comments with getDeviceIds

Addressing the following comments from NDK API council.
1. Available since API level 36 should not be the first line.
2. Comments about stream being Nonnull are not needed.
3. Both ids and numIds should be marked with Nullable.

Bug: 380300288
Test: atest AAudioTests
Flag: EXEMPT NDK
Change-Id: I0e2c00d46ceeb1039a016b4684013778f2fcef32