[FIR] Add CFG nodes, add multiple subGraphs for CFGOwner

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

@@ -9,7 +9,7 @@ val a: Int
         fun bar(): Int {
             val d: Int
             42
-            return d
+            return <!UNINITIALIZED_VARIABLE!>d<!>
         }
 
         return <!UNINITIALIZED_VARIABLE!>b<!>

compiler/testData/diagnostics/tests/controlFlowAnalysis/kt2960.fir.kt

@@ -15,13 +15,13 @@ val o = object {
         p.x = 4
 
         val z : Int
-        doSmth(<!UNINITIALIZED_VARIABLE!>z<!>)
+        doSmth(<!UNINITIALIZED_VARIABLE, UNINITIALIZED_VARIABLE!>z<!>)
     }
 }
 
 val g = { ->
     val x: Int
-    doSmth(x)
+    doSmth(<!UNINITIALIZED_VARIABLE!>x<!>)
 }
 
 class A {

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

@@ -1,7 +1,7 @@
 fun test1() {
     fun bar() {
         var i : Int
-        doSmth(i)
+        doSmth(<!UNINITIALIZED_VARIABLE!>i<!>)
     }
 }
 
@@ -16,7 +16,7 @@ fun test2() {
             doSmth(e)
         }
 
-        doSmth(s)
+        doSmth(<!UNINITIALIZED_VARIABLE!>s<!>)
     }
 }
 
@@ -40,7 +40,7 @@ fun test5() {
             fun inner3() {
                 fun inner4() {
                     val a : Int
-                    doSmth(a)
+                    doSmth(<!UNINITIALIZED_VARIABLE!>a<!>)
                 }
             }
         }