FIR: only allow member val initialization through this@T

class C {
    val x: Int
    init {
      // valid ways to initialize:
      x = 1
      this@C.x = 1
      // invalid:
      someOtherC.x = 1
      run { /*this@run.*/x = 1 }
      val self = this
      self.x = 1
    }
  }

compiler/testData/diagnostics/tests/controlFlowAnalysis/propertiesInitWithOtherInstanceInner.fir.kt

@@ -15,7 +15,7 @@ class Outer {
             innerProp = "6" // do not repeat the same diagnostic with this receiver
             this@Inner.innerProp = "7"
 
-            inner.innerProp = "8"
+            inner.<!VAL_REASSIGNMENT!>innerProp<!> = "8"
         }
     }
 }