Change parsing rules for primary constructor

- Parse 'constructor' keyword before value arguments
- Allow unescaped annotations

compiler/testData/psi/primaryConstructor/recoveryNestedClassAmbiguity.kt

@@ -0,0 +1,25 @@
+class Outer1 {
+    class Nested1
+
+    private Ann ()
+}
+
+class Outer2 {
+    class Nested2 private Ann
+    fun foo() {}
+}
+
+class Outer3 {
+    class Nested3 private Ann {}
+    fun foo()
+}
+
+class Outer4 {
+    class Nested3 private Ann() {}
+    fun foo()
+}
+
+class Outer4 {
+    class Nested3 private Ann() : Base()
+    fun foo()
+}