K2: Support Unit-typed synthetic Java property

^KT-57979 Fixed

compiler/testData/diagnostics/tests/j+k/properties/unitVsVoid.fir.kt

@@ -0,0 +1,44 @@
+// ISSUE: KT-57979
+
+// FILE: J.java
+import org.jetbrains.annotations.*;
+
+public class J<T> {
+    @Nullable
+    public T getValue1() {
+        return null;
+    }
+
+    public void setValue1(T value) {
+    }
+
+    @NotNull
+    public T getValue2() {
+        return null;
+    }
+
+    public void setValue2(T value) {
+    }
+
+    public T getValue3() {
+        return null;
+    }
+
+    public void setValue3(T value) {
+    }
+}
+// FILE: main.kt
+
+fun test(j: J<Unit>) {
+    j.value1 = Unit
+    j.value2 = Unit
+    j.value3 = Unit
+
+    j.value1 = null
+    j.value2 = <!NULL_FOR_NONNULL_TYPE!>null<!>
+    j.value3 = null
+
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Unit?")!>j.value1<!>
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Unit")!>j.value2<!>
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Unit..kotlin.Unit?!")!>j.value3<!>
+}

compiler/testData/diagnostics/tests/j+k/properties/unitVsVoid.kt

@@ -0,0 +1,44 @@
+// ISSUE: KT-57979
+
+// FILE: J.java
+import org.jetbrains.annotations.*;
+
+public class J<T> {
+    @Nullable
+    public T getValue1() {
+        return null;
+    }
+
+    public void setValue1(T value) {
+    }
+
+    @NotNull
+    public T getValue2() {
+        return null;
+    }
+
+    public void setValue2(T value) {
+    }
+
+    public T getValue3() {
+        return null;
+    }
+
+    public void setValue3(T value) {
+    }
+}
+// FILE: main.kt
+
+fun test(j: J<Unit>) {
+    j.value1 = Unit
+    j.value2 = Unit
+    j.value3 = Unit
+
+    j.value1 = null
+    j.value2 = <!NULL_FOR_NONNULL_TYPE!>null<!>
+    j.value3 = null
+
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Unit?")!>j.value1<!>
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Unit")!>j.value2<!>
+    <!DEBUG_INFO_EXPRESSION_TYPE("(kotlin.Unit..kotlin.Unit?)")!>j.value3<!>
+}