FIR: fix some errors in local variable assignment analyzer

* wrong method was called from FirDataFlowAnalyzer.exitFunctionCall;
 * map from function to affected properties should be keyed by symbol,
   not FirFunction, as the latter may change;
 * arguments of `return` and assignment statements should be visited,
   as they may contain lambdas.

compiler/testData/diagnostics/tests/smartCasts/kt30826.fir.kt

@@ -1,18 +0,0 @@
-// Issue: KT-30826
-
-interface I1
-interface I2 {
-    fun foo() {}
-}
-
-class A : I1, I2
-
-fun foo(x: I1?) {
-    var y = x
-    y as I2
-    val bar = {
-        y.foo() // NPE in NI, smartcast impossible in OI
-    }
-    y = null
-    bar()
-}

compiler/testData/diagnostics/tests/smartCasts/kt30826.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // Issue: KT-30826
 
 interface I1