FIR: Adjust override checker to definitely-not-nullable types

^KT-52201 Related

compiler/testData/diagnostics/tests/j+k/overrideWithErasure.kt

@@ -0,0 +1,20 @@
+// FIR_IDENTICAL
+// SKIP_TXT
+// FILE: Base.java
+public class Base<T extends CharSequence> {
+    public T foo(T t) { return t; }
+}
+
+// FILE: Derived.java
+public class Derived<E extends CharSequence> extends Base<E> {
+    @Override
+    public E foo(CharSequence e) {
+        return (E) "";
+    }
+}
+
+// FILE: main.kt
+
+fun main(d: Derived<CharSequence>) {
+    d.foo("")
+}

compiler/testData/loadJava/compiledJava/kotlinSignature/propagation/parameter/OverrideWithErasedParameter.fir.txt

@@ -2,8 +2,6 @@ public abstract interface OverrideWithErasedParameter : R|kotlin/Any| {
     public abstract interface Sub<T : R|ft<kotlin/Any, kotlin/Any?>|> : R|test/OverrideWithErasedParameter.Super<ft<T & Any, T?>>| {
         public abstract fun foo(o: R|ft<kotlin/Any, kotlin/Any?>|): R|kotlin/Unit|
 
-        public abstract fun foo(t: R|ft<T & Any, T?>|): R|kotlin/Unit|
-
     }
     public abstract interface Super<T : R|ft<kotlin/Any, kotlin/Any?>|> : R|kotlin/Any| {
         public abstract fun foo(t: R|ft<T & Any, T?>|): R|kotlin/Unit|