Add "Change to val" quick fix for MUST_BE_INITIALIZED

#KT-15723 Fixed

idea/testData/quickfix/variables/changeMutability/canBeVal/uninitializedWithGetter.kt

@@ -0,0 +1,5 @@
+// "Change to val" "true"
+class Test {
+    var foo<caret>
+        get() = 1
+}

idea/testData/quickfix/variables/changeMutability/canBeVal/uninitializedWithGetter.kt.after

@@ -0,0 +1,5 @@
+// "Change to val" "true"
+class Test {
+    val foo
+        get() = 1
+}

idea/testData/quickfix/variables/changeMutability/canBeVal/uninitializedWithGetter2.kt

@@ -0,0 +1,7 @@
+// "Change to val" "true"
+class Test {
+    var foo: Int<caret>
+        get() {
+            return 1
+        }
+}

idea/testData/quickfix/variables/changeMutability/canBeVal/uninitializedWithGetter2.kt.after

@@ -0,0 +1,7 @@
+// "Change to val" "true"
+class Test {
+    val foo: Int
+        get() {
+            return 1
+        }
+}

idea/testData/quickfix/variables/changeMutability/canBeVal/uninitializedWithGetter3.kt

@@ -0,0 +1,14 @@
+// "Change to val" "false"
+// ACTION: Add initializer
+// ACTION: Convert member to extension
+// ACTION: Initialize with constructor parameter
+// ACTION: Introduce backing property
+// ACTION: Move to companion object
+// ACTION: Specify type explicitly
+// ERROR: Property must be initialized
+class Test {
+    var foo<caret>
+        get() {
+            return 1
+        }
+}