[FIR] Support synthetic property setters

compiler/testData/diagnostics/tests/syntheticExtensions/javaProperties/AbbreviationName.fir.kt

@@ -1,7 +1,7 @@
 // FILE: KotlinFile.kt
 fun foo(javaClass: JavaClass) {
     javaClass.url = javaClass.url + "/"
-    javaClass.<!VARIABLE_EXPECTED!>htmlFile<!> += "1"
+    javaClass.htmlFile += "1"
 
     javaClass.<!UNRESOLVED_REFERENCE!>URL<!>
     javaClass.<!UNRESOLVED_REFERENCE!>uRL<!>

compiler/testData/diagnostics/tests/syntheticExtensions/javaProperties/GenericClass.fir.kt

@@ -1,6 +1,6 @@
 // FILE: KotlinFile.kt
 fun foo(javaClass: JavaClass<String>) {
-    javaClass.<!VARIABLE_EXPECTED!>something<!> += "x"
+    javaClass.something += "x"
 }
 
 // FILE: JavaClass.java

compiler/testData/diagnostics/tests/syntheticExtensions/javaProperties/KotlinOverridesJava.fir.kt

@@ -22,7 +22,7 @@ fun foo(k: KotlinClass) {
     useString(k.something3)
 
     k.setSomething4("")
-    k.<!VARIABLE_EXPECTED!>something4<!> += ""
+    k.something4 += ""
     k.<!INAPPLICABLE_CANDIDATE!>setSomething4<!>(null)
     k.something4 = null