managedCppForwarder function
A nitrogen link managed C++ source forwarder — used in both CocoaPods
Classes/ and SPM Sources/<Plugin>Cpp/ targets.
relativePath is the relative path from the forwarder to the source file.
Implementation
String managedCppForwarder(String relativePath) =>
'// Generated by nitrogen link — do not edit.\n'
'#include "$relativePath"\n';