Minor: add test for primary constructor default parameter values.

compiler/testData/ir/irText/declarations/primaryCtorDefaultArguments.kt

@@ -0,0 +1 @@
+class Test(val x: Int = 0)

compiler/testData/ir/irText/declarations/primaryCtorDefaultArguments.txt

@@ -0,0 +1,17 @@
+FILE /primaryCtorDefaultArguments.kt
+  CLASS CLASS Test
+    CONSTRUCTOR public constructor Test(x: kotlin.Int = ...)
+      x: EXPRESSION_BODY
+        CONST Int type=kotlin.Int value='0'
+      BLOCK_BODY
+        DELEGATING_CONSTRUCTOR_CALL 'constructor Any()'
+        INSTANCE_INITIALIZER_CALL classDescriptor='Test'
+    PROPERTY public final val x: kotlin.Int
+      FIELD public final val x: kotlin.Int
+        EXPRESSION_BODY
+          GET_VAR 'value-parameter x: Int = ...' type=kotlin.Int operator=INITIALIZE_PROPERTY_FROM_PARAMETER
+      FUN public final fun <get-x>(): kotlin.Int
+        BLOCK_BODY
+          RETURN type=kotlin.Nothing from='<get-x>(): Int'
+            GET_BACKING_FIELD 'x: Int' type=kotlin.Int operator=null
+              receiver: THIS of 'Test' type=Test