FIR: make declarations marked with 'override' implicitly open

#KT-52236 Fixed

compiler/fir/analysis-tests/testData/resolve/fromBuilder/enums.fir.txt

@@ -33,7 +33,7 @@ FILE: enums.kt
                 super<R|Planet|>(Double(1.0), Double(2.0))
             }
 
-            public final override fun sayHello(): R|kotlin/Unit| {
+            public open override fun sayHello(): R|kotlin/Unit| {
                 <Unresolved name: println>#(String(Hello!!!))
             }
 
@@ -44,7 +44,7 @@ FILE: enums.kt
                 super<R|Planet|>(Double(3.0), Double(4.0))
             }
 
-            public final override fun sayHello(): R|kotlin/Unit| {
+            public open override fun sayHello(): R|kotlin/Unit| {
                 <Unresolved name: println>#(String(Ola!!!))
             }
 
@@ -55,7 +55,7 @@ FILE: enums.kt
                 super<R|Planet|>(Double(5.0), Double(6.0))
             }
 
-            public final override fun sayHello(): R|kotlin/Unit| {
+            public open override fun sayHello(): R|kotlin/Unit| {
                 <Unresolved name: println>#(String(Privet!!!))
             }
 

compiler/fir/analysis-tests/testData/resolve/fromBuilder/simpleClass.fir.txt

@@ -14,11 +14,11 @@ FILE: simpleClass.kt
         private final val baz: R|kotlin/Int| = Int(42)
             private get(): R|kotlin/Int|
 
-        public final override fun foo(x: R|kotlin/Int|, y: R|kotlin/String|): R|kotlin/String| {
+        public open override fun foo(x: R|kotlin/Int|, y: R|kotlin/String|): R|kotlin/String| {
             ^foo R|<local>/y|.R|kotlin/String.plus|(R|<local>/x|).R|kotlin/String.plus|(this@R|/SomeClass|.R|/SomeClass.baz|)
         }
 
-        public final override var bar: R|kotlin/Boolean|
+        public open override var bar: R|kotlin/Boolean|
             public get(): R|kotlin/Boolean| {
                 ^ Boolean(true)
             }

compiler/fir/analysis-tests/testData/resolve/fromBuilder/typeParameters.fir.txt

@@ -18,11 +18,11 @@ FILE: typeParameters.kt
             super<R|AbstractList<kotlin/Int>|>()
         }
 
-        public final override operator fun get(index: R|kotlin/Int|): R|kotlin/Int| {
+        public open override operator fun get(index: R|kotlin/Int|): R|kotlin/Int| {
             ^get Int(42)
         }
 
-        public final override infix fun concat(other: R|List<kotlin/Int>|): R|List<kotlin/Int>| {
+        public open override infix fun concat(other: R|List<kotlin/Int>|): R|List<kotlin/Int>| {
             ^concat this@R|/SomeList|
         }