check Nothing type for all expressions not only for calls and simple names

(but excluding statement expressions)

compiler/testData/diagnostics/tests/controlFlowAnalysis/DeadCode.kt

@@ -0,0 +1,23 @@
+package c
+
+fun test1() {
+    <!UNREACHABLE_CODE!>val <!UNUSED_VARIABLE!>r<!>: Nothing = null!!<!>
+}
+
+fun test2(a: A) {
+    a + a
+    <!UNREACHABLE_CODE!>bar()<!>
+}
+
+fun test3() {
+    null!!
+    <!UNREACHABLE_CODE!>bar()<!>
+}
+
+fun throwNPE() = null!!
+
+class A {
+    fun plus(<!UNUSED_PARAMETER!>a<!>: A): Nothing = throw Exception()
+}
+
+fun bar() {}