FoldInitializerAndIfToElvisInspection: don't add explicit type if var is used as non-nullable

#KT-38349 Fixed

idea/testData/inspectionsLocal/foldInitializerAndIfToElvis/VarUsedAsNotNullable.kt

@@ -1,4 +1,3 @@
-// PROBLEM: none
 fun test(foo: Int?, bar: Int): Int {
     var i = foo
     <caret>if (i == null) {

idea/testData/inspectionsLocal/foldInitializerAndIfToElvis/VarUsedAsNotNullable.kt.after

@@ -0,0 +1,4 @@
+fun test(foo: Int?, bar: Int): Int {
+    var i = foo ?: return bar
+    return i
+}

idea/testData/inspectionsLocal/foldInitializerAndIfToElvis/VarUsedAsNotNullable2.kt

@@ -1,4 +1,3 @@
-// PROBLEM: none
 fun test(foo: Int?, bar: Int): Int {
     var i = foo
     <caret>if (i == null) {

idea/testData/inspectionsLocal/foldInitializerAndIfToElvis/VarUsedAsNotNullable2.kt.after

@@ -0,0 +1,8 @@
+fun test(foo: Int?, bar: Int): Int {
+    var i = foo ?: return bar
+    baz(i)
+    val j = i + 1
+    return j
+}
+
+fun baz(i: Int?) {}