Fix corner cases (override/script/null/etc.) in "might be const"

Related to KT-20644

idea/testData/inspectionsLocal/mayBeConstant/constInExpr.kt

@@ -0,0 +1,2 @@
+const val first = 1
+val sec<caret>ond = first * 2

idea/testData/inspectionsLocal/mayBeConstant/constInExpr.kt.after

@@ -0,0 +1,2 @@
+const val first = 1
+const val second = first * 2

idea/testData/inspectionsLocal/mayBeConstant/nonConstInExpr.kt

@@ -0,0 +1,4 @@
+// PROBLEM: none
+
+val first = 1
+val sec<caret>ond = first * 2

idea/testData/inspectionsLocal/mayBeConstant/null.kt

@@ -0,0 +1,3 @@
+// PROBLEM: none
+
+val no<caret>thing = null

idea/testData/inspectionsLocal/mayBeConstant/override.kt

@@ -0,0 +1,9 @@
+// PROBLEM: none
+
+interface Base {
+    val property: Int
+}
+
+object Derived : Base {
+    override val prop<caret>erty = 42
+}

idea/testData/inspectionsLocal/mayBeConstant/script.kts

@@ -0,0 +1,3 @@
+// PROBLEM: none
+
+val top<caret>Script = 1