Report ILLEGAL_MODIFIER on inappropriate 'inner' keyword usage

#KT-1174 In Progress

compiler/testData/diagnostics/tests/inner/illegalModifier.kt

@@ -0,0 +1,41 @@
+<!ILLEGAL_MODIFIER!>inner<!> fun foo() {}
+<!ILLEGAL_MODIFIER!>inner<!> val prop = 42
+
+<!ILLEGAL_MODIFIER!>inner<!> class A
+<!ILLEGAL_MODIFIER!>inner<!> trait B
+<!ILLEGAL_MODIFIER!>inner<!> object C
+
+class D {
+    inner class E
+    <!ILLEGAL_MODIFIER!>inner<!> trait F
+    <!ILLEGAL_MODIFIER!>inner<!> object G
+    <!ILLEGAL_MODIFIER!>inner<!> enum class R
+    <!ILLEGAL_MODIFIER!>inner<!> annotation class S
+    <!ILLEGAL_MODIFIER!>inner<!> class object
+}
+
+enum class H {
+    <!ILLEGAL_MODIFIER!>inner<!> I {
+        inner class II
+    }
+    
+    inner class J
+}
+
+trait K {
+    <!ILLEGAL_MODIFIER!>inner<!> class L
+}
+
+object N {
+    inner class O
+}
+
+class P {
+    class object {
+        inner class Q
+    }
+}
+
+val R = object {
+    inner class S
+}