FIR: make declarations marked with 'override' implicitly open

#KT-52236 Fixed

compiler/fir/analysis-tests/testData/resolve/problems/compilerPhase.fir.txt

@@ -30,7 +30,7 @@ FILE: compilerPhase.kt
         private/*private to this*/ final val lower: R|CompilerPhase<Context, Data, Data>| = R|<local>/lower|
             private/*private to this*/ get(): R|CompilerPhase<Context, Data, Data>|
 
-        public final override fun invoke(phaseConfig: R|PhaseConfig|, phaserState: R|PhaserState<Data>|, context: R|Context|, input: R|Data|): R|Data| {
+        public open override fun invoke(phaseConfig: R|PhaseConfig|, phaserState: R|PhaserState<Data>|, context: R|Context|, input: R|Data|): R|Data| {
             lval output: R|Data| = when () {
                 R|<local>/phaseConfig|.R|/PhaseConfig.needProfiling| ->  {
                     this@R|/NamedCompilerPhase|.R|/NamedCompilerPhase.runAndProfile|(R|<local>/phaseConfig|, R|<local>/phaserState|, R|<local>/context|, R|<local>/input|)

compiler/fir/analysis-tests/testData/resolve/problems/defaultParametersFromDifferentScopes.fir.txt

@@ -12,7 +12,7 @@ FILE: defaultParametersFromDifferentScopes.kt
             super<R|kotlin/Any|>()
         }
 
-        public final override fun some(x: R|kotlin/Int|, y: R|kotlin/Int|): R|kotlin/Unit| {
+        public open override fun some(x: R|kotlin/Int|, y: R|kotlin/Int|): R|kotlin/Unit| {
         }
 
     }

compiler/fir/analysis-tests/testData/resolve/problems/inaccessibleJavaGetter.fir.txt

@@ -12,12 +12,12 @@ FILE: test.kt
             super<R|kotlin/Any|>()
         }
 
-        public final override val setter: R|kotlin/String|
+        public open override val setter: R|kotlin/String|
             public get(): R|kotlin/String| {
                 ^ String(K)
             }
 
-        public final override val isDelegated: R|kotlin/Boolean|
+        public open override val isDelegated: R|kotlin/Boolean|
             public get(): R|kotlin/Boolean| {
                 ^ Boolean(false)
             }