[FIR] RHS assignment during equality comparison should invalidate DFA

If the right-hand side of an equality comparison contains an assignment
to the variable used in the left-hand side, then implications about the
equality comparison within data-flow analysis cannot be applied, as the
value of the variable will be different after the comparison.

^KT-55096 Fixed

compiler/testData/diagnostics/tests/smartCasts/variables/reassignedInRhs.fir.kt

@@ -27,9 +27,9 @@ fun unoverriddenEquals(a: Any?) {
     var b: Any?
     b = c
     if (b == c.also { b = a }) {
-        a.x // bad (b#0 is C, b#1 = a)
-        b.x // bad (b#0 is C, this is b#1)
-        if (<!USELESS_IS_CHECK!>b is C<!>) { // b#1
+        a.<!UNRESOLVED_REFERENCE!>x<!> // bad (b#0 is C, b#1 = a)
+        b.<!UNRESOLVED_REFERENCE!>x<!> // bad (b#0 is C, this is b#1)
+        if (b is C) { // b#1
             a.x // ok (b#1 = a)
             b.x // ok
         }