[GR-10977] [GR-10799] Unify possible results of R2Foreign.

CHANGELOG.md

...ngine/src/com/oracle/truffle/r/engine/EngineRootNode.java

...ngine/src/com/oracle/truffle/r/engine/interop/ListMR.java

...ruffle/r/engine/interop/RAbstractVectorAccessFactory.java

...racle/truffle/r/engine/interop/RArgsValuesAndNamesMR.java

...c/com/oracle/truffle/r/engine/interop/REnvironmentMR.java

...e/truffle/r/engine/interop/RForeignAccessFactoryImpl.java

.../src/com/oracle/truffle/r/engine/interop/RFunctionMR.java

...src/com/oracle/truffle/r/engine/interop/RInteropNAMR.java

...e/src/com/oracle/truffle/r/engine/interop/RLogicalMR.java

.../src/com/oracle/truffle/r/engine/interop/RS4ObjectMR.java

...om/oracle/truffle/r/nodes/builtin/fastr/FastRInterop.java

...src/com/oracle/truffle/r/runtime/data/RInteropScalar.java

...e/src/com/oracle/truffle/r/runtime/interop/Foreign2R.java

...e/src/com/oracle/truffle/r/runtime/interop/R2Foreign.java

...c/com/oracle/truffle/r/test/tck/RTCKLanguageProvider.java

.../oracle/truffle/r/test/engine/interop/AbstractMRTest.java

.../com/oracle/truffle/r/test/engine/interop/ListMRTest.java

...ffle/r/test/engine/interop/RArgsValuesAndNamesMRTest.java

...cle/truffle/r/test/engine/interop/REnvironmentMRTest.java