FIR: Add separate local scopes for blocks

compiler/testData/codegen/box/functions/localFunctions/nameClashAcrossDifferentContainers.kt

@@ -1,5 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
-
 var result = ""
 
 fun overload() {

compiler/testData/diagnostics/tests/controlFlowAnalysis/initializationInLambda.fir.kt

@@ -70,8 +70,8 @@ class Your {
 val z = if (true) {
     val xx: Int
     exec {
-        <!UNRESOLVED_REFERENCE!>xx<!> = 24
+        xx = 24
     }
     42
 }
-else 0
+else 0