Add new diagnostic tests to check new rules for const modifier

compiler/testData/diagnostics/tests/modifiers/const/ifConstVal.kt

@@ -0,0 +1,22 @@
+const val flag = true
+const val value = 10
+
+const val condition = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>if (flag) "True" else "Error"<!>
+const val withWhen = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>when (flag) {
+    true -> "True"
+    else -> "Error"
+}<!>
+const val withWhen2 = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>when {
+    flag == true -> "True"
+    else -> "Error"
+}<!>
+const val withWhen3 = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>when(value) {
+    10 -> "1"
+    100 -> "2"
+    else -> "3"
+}<!>
+const val multibranchIf = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>if (value == 100) 1 else if (value == 1000) 2 else 3<!>
+
+val nonConstFlag = true
+const val errorConstIf = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>if (nonConstFlag) 1 else 2<!>
+const val errorBranch = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>if (flag) nonConstFlag else false<!>