Let PolyglotModuleBuiltins#postInitialize load _polyglot.py and don't force to load polyglot at startup

(cherry picked from commit 8bfdf10)

Fix conflict

Author: eregon

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/Python3Core.java

@@ -1069,9 +1069,6 @@ public void run() {
                 }
             }
 
-            // import polyglot decorators and special interop predefined behavior
-            loadFile(toTruffleStringUncached("_polyglot"), getContext().getCoreHomeOrFail());
-
             initialized = true;
         }
     }

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/PolyglotModuleBuiltins.java

@@ -113,6 +113,7 @@
 import com.oracle.graal.python.nodes.interop.InteropBehaviorMethod;
 import com.oracle.graal.python.nodes.interop.PForeignToPTypeNode;
 import com.oracle.graal.python.nodes.object.GetForeignObjectClassNode;
+import com.oracle.graal.python.nodes.statement.AbstractImportNode;
 import com.oracle.graal.python.nodes.truffle.PythonArithmeticTypes;
 import com.oracle.graal.python.nodes.util.CannotCastException;
 import com.oracle.graal.python.nodes.util.CastToJavaStringNode;
@@ -161,6 +162,7 @@ public final class PolyglotModuleBuiltins extends PythonBuiltins {
     private static final TruffleString T_MODIFIABLE = tsLiteral("modifiable");
     private static final TruffleString T_INVOKABLE = tsLiteral("invokable");
     private static final TruffleString T_INTERNAL = tsLiteral("internal");
+    private static final TruffleString T_INTERNAL_POLYGLOT_MODULE = tsLiteral("_polyglot");
 
     @Override
     protected List<com.oracle.truffle.api.dsl.NodeFactory<? extends PythonBuiltinBaseNode>> getNodeFactories() {
@@ -189,6 +191,9 @@ public void postInitialize(Python3Core core) {
         super.postInitialize(core);
 
         GetForeignObjectClassNode.getUncached().defineSingleTraitClasses();
+
+        // import polyglot decorators which are defined in Python code
+        AbstractImportNode.importModule(T_INTERNAL_POLYGLOT_MODULE);
     }
 
     @Builtin(name = "import_value", minNumOfPositionalArgs = 1, parameterNames = {"name"})