[FIR] UNREACHABLE_CODE diagnostic (wip)

Implementation for PSI only

compiler/testData/diagnostics/tests/controlFlowAnalysis/deadCode/deadCodeInArrayAccess.fir.kt

@@ -1,40 +1,40 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 fun testArrayAccess1(array: Array<Any>) {
-    array[todo()]
+    array<!UNREACHABLE_CODE!>[<!>todo()<!UNREACHABLE_CODE!>]<!>
 }
 
 fun testArrayAccess2() {
     operator fun Nothing.get(i: Int, s: String) {}
-    todo()[1, ""]
+    todo()<!UNREACHABLE_CODE!>[1, ""]<!>
 }
 
 fun testAraryAccess3() {
     operator fun Nothing.get(n: Nothing) {}
-    todo()[todo()]
+    todo()<!UNREACHABLE_CODE!>[todo()]<!>
 }
 
 fun testArrayAssignment1(array: Array<Any>) {
-    array[todo()] = 11
+    array<!UNREACHABLE_CODE!>[<!>todo()<!UNREACHABLE_CODE!>] = 11<!>
 }
 
 fun testArrayAssignment2(array: Array<Any>) {
-    array[1] = todo()
+    array<!UNREACHABLE_CODE!>[<!>1<!UNREACHABLE_CODE!>] =<!> todo()
 }
 
 fun testArrayAssignment3(n: Nothing) {
     operator fun Nothing.set(i: Int, j: Int) {}
-    n[1] = 2
+    n<!UNREACHABLE_CODE!>[1] = 2<!>
 }
 
 fun testArrayAssignment4(n: Nothing) {
     operator fun Nothing.set(i: Int, a: Any) {}
-    n[1] = todo()
+    n<!UNREACHABLE_CODE!>[1] = todo()<!>
 }
 
 fun testArrayPlusAssign(array: Array<Any>) {
     operator fun Any.plusAssign(a: Any) {}
-    array[1] += todo()
+    array<!UNREACHABLE_CODE!>[<!>1<!UNREACHABLE_CODE!>] +=<!> todo()
 }
 
-fun todo(): Nothing = throw Exception()
+fun todo(): Nothing = throw Exception()