To resolve build issue after updating Xcode from 15.2 to 15.3.
Specifically, looks like there a number of changes to C++ Standard Library: https://developer.apple.com/documentation/xcode-release-notes/xcode-15_3-release-notes#C++-Standard-Library
The relevant piece might be:
The <experimental/algorithm> and <experimental/functional> headers have been removed, since all the contents have been implemented in namespace std.
We weren't previously including <experimental/functional>, but now it requires us to include <functional> in order for it to recognize std::function.
We include <functional> elsewhere in the codebase, so maybe it was getting resolved by coincidence or something in the past? Either way, this change fixes the iOS build.
Depends on D11261