FIR: make declarations marked with 'override' implicitly open

#KT-52236 Fixed

compiler/fir/analysis-tests/testData/resolve/visibility/exposedFunctionReturnType.fir.txt

@@ -30,7 +30,7 @@ FILE: exposedFunctionReturnType.kt
                 super<R|Some|>()
             }
 
-            public final override fun foo(): R|Some| {
+            public open override fun foo(): R|Some| {
                 ^foo R|/Some.FIRST|
             }
 

compiler/fir/analysis-tests/testData/resolve/visibility/intersectionOverrideWithImplicitTypes.fir.txt

@@ -8,7 +8,7 @@ FILE: intersectionOverrideWithImplicitTypes.kt
             super<R|kotlin/Any|>()
         }
 
-        public final override fun <T, R> foo(value: R|T|, producer: R|(T) -> R|): R|R| {
+        public open override fun <T, R> foo(value: R|T|, producer: R|(T) -> R|): R|R| {
             ^foo Null(null)!!
         }
 

compiler/fir/analysis-tests/testData/resolve/visibility/kotlinJavaKotlinHierarchy.fir.txt

@@ -4,7 +4,7 @@ FILE: C.kt
             super<R|B|>()
         }
 
-        public final override fun foo(): R|kotlin/Unit| {
+        public open override fun foo(): R|kotlin/Unit| {
         }
 
     }

compiler/fir/analysis-tests/testData/resolve/visibility/visibilityWithOverrides.fir.txt

@@ -4,7 +4,7 @@ FILE: B.kt
             super<R|A|>()
         }
 
-        protected final override infix fun foo(s: R|kotlin/String|): R|kotlin/String| {
+        protected open override infix fun foo(s: R|kotlin/String|): R|kotlin/String| {
             ^foo String()
         }