[GR-8922] Fake registration of RFunction-s as if native functions.

...ffle/r/ffi/impl/llvm/TruffleLLVM_DownCallNodeFactory.java

.../com/oracle/truffle/r/nodes/builtin/base/BasePackage.java

...oracle/truffle/r/nodes/builtin/base/DynLoadFunctions.java

.../nodes/builtin/base/foreign/CallAndExternalFunctions.java

...le/r/nodes/builtin/base/foreign/FortranAndCFunctions.java

...ffle/r/nodes/builtin/base/printer/ExternalPtrPrinter.java

...truffle/r/nodes/builtin/fastr/FastRRegisterFunctions.java

...e.r.runtime/src/com/oracle/truffle/r/runtime/ffi/DLL.java

...est/src/com/oracle/truffle/r/test/ExpectedTestOutput.test

...fle/r/test/library/base/foreign/TestRegisterFunction.java