FoldInitializerAndIfToElvisInspection: don't report when 'var' variable has no explicit type and it's used as not nullable type

#KT-38349 Fixed

idea/testData/inspectionsLocal/foldInitializerAndIfToElvis/VarUsedAsNotNullable.kt

@@ -0,0 +1,8 @@
+// PROBLEM: none
+fun test(foo: Int?, bar: Int): Int {
+    var i = foo
+    <caret>if (i == null) {
+        return bar
+    }
+    return i
+}

idea/testData/inspectionsLocal/foldInitializerAndIfToElvis/VarUsedAsNotNullable2.kt

@@ -0,0 +1,12 @@
+// PROBLEM: none
+fun test(foo: Int?, bar: Int): Int {
+    var i = foo
+    <caret>if (i == null) {
+        return bar
+    }
+    baz(i)
+    val j = i + 1
+    return j
+}
+
+fun baz(i: Int?) {}

idea/testData/inspectionsLocal/foldInitializerAndIfToElvis/VarUsedAsNullable.kt

@@ -0,0 +1,7 @@
+fun test(foo: Int?, bar: Int): Int? {
+    var i = foo
+    <caret>if (i == null) {
+        return bar
+    }
+    return i
+}

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

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

idea/testData/inspectionsLocal/foldInitializerAndIfToElvis/VarUsedAsNullable2.kt

@@ -0,0 +1,9 @@
+fun test(foo: Int?, bar: Int): Int {
+    var i = foo
+    <caret>if (i == null) {
+        return bar
+    }
+    return baz(i)
+}
+
+fun baz(i: Int?) = 1

idea/testData/inspectionsLocal/foldInitializerAndIfToElvis/VarUsedAsNullable2.kt.after

@@ -0,0 +1,6 @@
+fun test(foo: Int?, bar: Int): Int {
+    var i: Int? = foo ?: return bar
+    return baz(i)
+}
+
+fun baz(i: Int?) = 1