Use back-ticks correctly in "Add remaining branches" action

So #KT-13985 Fixed

idea/testData/quickfix/when/addRemainingBranchesEnumBackTicks.kt

@@ -0,0 +1,10 @@
+// "Add remaining branches" "true"
+// WITH_RUNTIME
+
+enum class FooEnum {
+    A, B, `C`, `true`, `false`, `null`
+}
+
+fun test(foo: FooEnum?) = <caret>when (foo) {
+    FooEnum.A -> "A"
+}

idea/testData/quickfix/when/addRemainingBranchesEnumBackTicks.kt.after

@@ -0,0 +1,16 @@
+// "Add remaining branches" "true"
+// WITH_RUNTIME
+
+enum class FooEnum {
+    A, B, `C`, `true`, `false`, `null`
+}
+
+fun test(foo: FooEnum?) = <caret>when (foo) {
+    FooEnum.A -> "A"
+    FooEnum.B -> TODO()
+    FooEnum.C -> TODO()
+    FooEnum.`true` -> TODO()
+    FooEnum.`false` -> TODO()
+    FooEnum.`null` -> TODO()
+    null -> TODO()
+}

idea/testData/quickfix/when/addRemainingBranchesSealedBackTicks.kt

@@ -0,0 +1,15 @@
+// "Add remaining branches" "true"
+// WITH_RUNTIME
+
+sealed class FooSealed
+object A: FooSealed()
+object B: FooSealed()
+object `C`: FooSealed()
+class D: FooSealed()
+class `true`: FooSealed()
+class `false`: FooSealed()
+object `null`: FooSealed()
+
+fun test(foo: FooSealed?) = <caret>when (foo) {
+    A -> "A"
+}

idea/testData/quickfix/when/addRemainingBranchesSealedBackTicks.kt.after

@@ -0,0 +1,22 @@
+// "Add remaining branches" "true"
+// WITH_RUNTIME
+
+sealed class FooSealed
+object A: FooSealed()
+object B: FooSealed()
+object `C`: FooSealed()
+class D: FooSealed()
+class `true`: FooSealed()
+class `false`: FooSealed()
+object `null`: FooSealed()
+
+fun test(foo: FooSealed?) = <caret>when (foo) {
+    A -> "A"
+    B -> TODO()
+    C -> TODO()
+    is D -> TODO()
+    is `true` -> TODO()
+    is `false` -> TODO()
+    `null` -> TODO()
+    null -> TODO()
+}