Platform: add APINotes for `bionic.spawn`
Add some APINotes for `bionic.spawn` to correct the nullability
annotations. This allows building Foundation with NDK r26b.
(cherry picked from commit c4f5831507760380e67671a7c43f4d36ae6e88f0)
(cherry picked from commit 9f8eaa4f4c35d3a04510a8905c1799c37d732680)
