[FIR] Support of REDECLARATION for local val/var, ^KT-54405 Fixed

compiler/fir/analysis-tests/testData/resolve/exhaustiveness/negative/missingBooleanBranch.fir.txt

@@ -32,7 +32,7 @@ FILE: missingBooleanBranch.kt
             }
         }
 
-        lval x: R|kotlin/Int| = when (R|<local>/cond|) {
+        lval y: R|kotlin/Int| = when (R|<local>/cond|) {
             ==($subj$, Boolean(true)) ->  {
                 Int(1)
             }

compiler/fir/analysis-tests/testData/resolve/exhaustiveness/negative/missingBooleanBranch.kt

@@ -19,7 +19,7 @@ fun test_2(cond: Boolean?) {
         false -> 2
     }
 
-    val x = when (cond) {
+    val y = when (cond) {
         true -> 1
         false -> 2
         null -> 3