Add possibility to interpret and fold IrStringConcatenation expression

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java

@@ -21229,6 +21229,12 @@ public class FirLightTreeOldFrontendDiagnosticsTestGenerated extends AbstractFir
                     runTest("compiler/testData/diagnostics/tests/modifiers/const/stdlibConstFun.kt");
                 }
 
+                @Test
+                @TestMetadata("stringConcatenation.kt")
+                public void testStringConcatenation() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/modifiers/const/stringConcatenation.kt");
+                }
+
                 @Test
                 @TestMetadata("stringConcatenationWithObject.kt")
                 public void testStringConcatenationWithObject() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java

@@ -21235,6 +21235,12 @@ public class FirPsiOldFrontendDiagnosticsTestGenerated extends AbstractFirPsiDia
                     runTest("compiler/testData/diagnostics/tests/modifiers/const/stdlibConstFun.kt");
                 }
 
+                @Test
+                @TestMetadata("stringConcatenation.kt")
+                public void testStringConcatenation() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/modifiers/const/stringConcatenation.kt");
+                }
+
                 @Test
                 @TestMetadata("stringConcatenationWithObject.kt")
                 public void testStringConcatenationWithObject() throws Exception {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirConstChecks.kt

@@ -79,7 +79,7 @@ internal fun checkConstantArguments(
                 if (exp is FirResolvedQualifier) {
                     return ConstantArgumentKind.NOT_CONST
                 }
-                checkConstantArguments(exp, session).let { return it }
+                checkConstantArguments(exp, session)?.let { return it }
             }
         }
         expression is FirGetClassCall -> {

compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirLightTreeBlackBoxCodegenTestGenerated.java

@@ -28388,6 +28388,12 @@ public class FirLightTreeBlackBoxCodegenTestGenerated extends AbstractFirLightTr
                 runTest("compiler/testData/codegen/box/involvesIrInterpreter/dumpIrAndCheck/stdlibConst.kt");
             }
 
+            @Test
+            @TestMetadata("stringConcatenation.kt")
+            public void testStringConcatenation() throws Exception {
+                runTest("compiler/testData/codegen/box/involvesIrInterpreter/dumpIrAndCheck/stringConcatenation.kt");
+            }
+
             @Test
             @TestMetadata("stringOperations.kt")
             public void testStringOperations() throws Exception {

compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirPsiBlackBoxCodegenTestGenerated.java

@@ -28388,6 +28388,12 @@ public class FirPsiBlackBoxCodegenTestGenerated extends AbstractFirPsiBlackBoxCo
                 runTest("compiler/testData/codegen/box/involvesIrInterpreter/dumpIrAndCheck/stdlibConst.kt");
             }
 
+            @Test
+            @TestMetadata("stringConcatenation.kt")
+            public void testStringConcatenation() throws Exception {
+                runTest("compiler/testData/codegen/box/involvesIrInterpreter/dumpIrAndCheck/stringConcatenation.kt");
+            }
+
             @Test
             @TestMetadata("stringOperations.kt")
             public void testStringOperations() throws Exception {