Extraction Engine: Suggest both bounds for nullability-flexible types without nullability annotations. Do not omit return type if inferred one is flexible

#KT-6837 Fixed

idea/testData/refactoring/extractFunction/basic/callWithPlatformTypeReceiver.kt

@@ -1,4 +1,5 @@
 // WITH_RUNTIME
+// SUGGESTED_RETURN_TYPES: kotlin.Boolean?, kotlin.Boolean
 // PARAM_DESCRIPTOR: value-parameter val it: kotlin.Map.Entry<(Boolean..Boolean?), (Boolean..Boolean?)> defined in test.<anonymous>
 // PARAM_TYPES: kotlin.Map.Entry<(Boolean..Boolean?), (Boolean..Boolean?)>
 fun test() {

idea/testData/refactoring/extractFunction/basic/callWithPlatformTypeReceiver.kt.after

@@ -1,8 +1,9 @@
 // WITH_RUNTIME
+// SUGGESTED_RETURN_TYPES: kotlin.Boolean?, kotlin.Boolean
 // PARAM_DESCRIPTOR: value-parameter val it: kotlin.Map.Entry<(Boolean..Boolean?), (Boolean..Boolean?)> defined in test.<anonymous>
 // PARAM_TYPES: kotlin.Map.Entry<(Boolean..Boolean?), (Boolean..Boolean?)>
 fun test() {
     J.getMap().filter { b(it) }
 }
 
-private fun b(it: Map.Entry<Boolean, Boolean>) = it.getKey()
+private fun b(it: Map.Entry<Boolean, Boolean>): Boolean? = it.getKey()

idea/testData/refactoring/extractFunction/controlFlow/returnTypeCandidates/javaAnnotatedNotNull.java

@@ -0,0 +1,8 @@
+import org.jetbrains.annotations.NotNull;
+
+public class J {
+    @NotNull
+    static String notNull() {
+        return "";
+    }
+}

idea/testData/refactoring/extractFunction/controlFlow/returnTypeCandidates/javaAnnotatedNotNull.kt

@@ -0,0 +1,5 @@
+// WITH_RUNTIME
+// SUGGESTED_NAMES: s, getS
+fun test() {
+    val s = <selection>J.notNull()</selection>
+}

idea/testData/refactoring/extractFunction/controlFlow/returnTypeCandidates/javaAnnotatedNotNull.kt.after

@@ -0,0 +1,7 @@
+// WITH_RUNTIME
+// SUGGESTED_NAMES: s, getS
+fun test() {
+    val s = s()
+}
+
+private fun s(): String = J.notNull()

idea/testData/refactoring/extractFunction/controlFlow/returnTypeCandidates/javaAnnotatedNullable.java

@@ -0,0 +1,8 @@
+import org.jetbrains.annotations.Nullable;
+
+public class J {
+    @Nullable
+    static String nullable() {
+        return null;
+    }
+}

idea/testData/refactoring/extractFunction/controlFlow/returnTypeCandidates/javaAnnotatedNullable.kt

@@ -0,0 +1,4 @@
+// SUGGESTED_NAMES: s, getS
+fun test() {
+    val s = <selection>J.nullable()</selection>
+}

idea/testData/refactoring/extractFunction/controlFlow/returnTypeCandidates/javaAnnotatedNullable.kt.after

@@ -0,0 +1,6 @@
+// SUGGESTED_NAMES: s, getS
+fun test() {
+    val s = s()
+}
+
+private fun s(): String? = J.nullable()

idea/testData/refactoring/extractFunction/controlFlow/returnTypeCandidates/javaNoNullabilityAnnotation.java

@@ -0,0 +1,5 @@
+public class J {
+    static String unknown() {
+        return "";
+    }
+}

idea/testData/refactoring/extractFunction/controlFlow/returnTypeCandidates/javaNoNullabilityAnnotation.kt

@@ -0,0 +1,5 @@
+// SUGGESTED_NAMES: s, getS
+// SUGGESTED_RETURN_TYPES: kotlin.String?, kotlin.String
+fun test() {
+    val s = <selection>J.unknown()</selection>
+}

idea/testData/refactoring/extractFunction/controlFlow/returnTypeCandidates/javaNoNullabilityAnnotation.kt.after

@@ -0,0 +1,7 @@
+// SUGGESTED_NAMES: s, getS
+// SUGGESTED_RETURN_TYPES: kotlin.String?, kotlin.String
+fun test() {
+    val s = s()
+}
+
+private fun s(): String? = J.unknown()

idea/testData/refactoring/extractFunction/typeParameters/typeParameterNotResolvableInTargetScope.kt.after

@@ -15,4 +15,4 @@ class Foo<T> {
     }
 }
 
-private fun <T> Foo<T>.t(l: String) = map[l]
+private fun <T> Foo<T>.t(l: String): T = map[l]

idea/testData/refactoring/extractFunction/typeParameters/typeParameterResolvableInTargetScope.kt.after

@@ -11,5 +11,5 @@ class Foo<T> {
         return t(l)
     }
 
-    private fun t(l: String) = map[l]
+    private fun t(l: String): T = map[l]
 }