Drop suppport for annotation syntax without '@' from parser

compiler/testData/diagnostics/tests/annotations/kt1860-negative.kt

@@ -1,9 +1,9 @@
-fun foo(<!UNRESOLVED_REFERENCE!><!SYNTAX!><!>varargs<!> <!UNUSED_PARAMETER!>f<!> : Int) {}
+fun foo(<!UNRESOLVED_REFERENCE!>@varargs<!> <!UNUSED_PARAMETER!>f<!> : Int) {}
 
 var bar : Int = 1
-  set(<!UNRESOLVED_REFERENCE!><!SYNTAX!><!>varargs<!> v) {}
+  set(<!UNRESOLVED_REFERENCE!>@varargs<!> v) {}
 
 val x : (Int) -> Int = {<!UNRESOLVED_REFERENCE!>@varargs<!> <!TYPE_MISMATCH!>x<!> <!SYNTAX!>: Int -> x<!>}
 
-class Hello(<!UNRESOLVED_REFERENCE!><!SYNTAX!><!>varargs<!> <!UNUSED_PARAMETER!>args<!>: Any) {
+class Hello(<!UNRESOLVED_REFERENCE!>@varargs<!> <!UNUSED_PARAMETER!>args<!>: Any) {
 }

compiler/testData/diagnostics/tests/imports/SyntaxError.kt

@@ -57,4 +57,4 @@ import a.<!SYNTAX!>%<!>.b.<!PACKAGE_CANNOT_BE_IMPORTED!>c<!>.<!SYNTAX!><!>
 import a.b.c.D.<!SYNTAX!><!>
 import a.b.c.D.E.<!SYNTAX!><!>
 
-import <!PACKAGE_CANNOT_BE_IMPORTED!>a<!><!SYNTAX!>?.<!><!UNRESOLVED_REFERENCE!><!SYNTAX!><!>b<!SYNTAX!><!><!>
+import <!PACKAGE_CANNOT_BE_IMPORTED!>a<!><!SYNTAX!>?.<!><!SYNTAX!>b<!>

compiler/testData/diagnostics/tests/recovery/namelessMembers.kt

@@ -12,6 +12,6 @@ class C {
     enum class<!SYNTAX!><!> {}
 }
 
-class C1<in<!SYNTAX!>><!><!SYNTAX!><!> {}
+class C1<<!SYNTAX!>in<!>> {}
 
 class C2(val<!SYNTAX!><!>) {}

compiler/testData/diagnostics/tests/recovery/namelessMembers.txt

@@ -31,8 +31,8 @@ public final class C {
     }
 }
 
-public final class C1</*0*/ in <no name provided>> {
-    public constructor C1</*0*/ in <no name provided>>()
+public final class C1</*0*/ <no name provided>> {
+    public constructor C1</*0*/ <no name provided>>()
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String

compiler/testData/diagnostics/tests/regressions/ea66984.kt

@@ -1,2 +1,2 @@
 // !DIAGNOSTICS: -NO_VALUE_FOR_PARAMETER
-class Tree<T>(<!NOT_A_CLASS!><!SYNTAX!><!>T<!> element<!SYNTAX!><!>, <!NOT_AN_ANNOTATION_CLASS!><!SYNTAX!><!>Tree<T><!> left<!SYNTAX!><!>, <!NOT_AN_ANNOTATION_CLASS!><!SYNTAX!><!>Tree<T><!> right<!SYNTAX!><!>) {}
+class Tree<<!REDECLARATION!>T<!>>(T <!SYNTAX!>element<!>, <!REDECLARATION, REDECLARATION!><!SYNTAX!><!>Tree<T><!><!SYNTAX!><!> left<!SYNTAX!><!>, <!REDECLARATION, REDECLARATION!><!SYNTAX!><!>Tree<T><!><!SYNTAX!><!> right<!SYNTAX!><!>) {}

compiler/testData/diagnostics/tests/regressions/ea66984.txt

@@ -1,7 +1,7 @@
 package
 
 public final class Tree</*0*/ T> {
-    public constructor Tree</*0*/ T>(/*0*/ @[ERROR : Not an annotation: T]() element: [ERROR : Type annotation was missing for parameter element], /*1*/ @Tree<T>() left: [ERROR : Type annotation was missing for parameter left], /*2*/ @Tree<T>() right: [ERROR : Type annotation was missing for parameter right])
+    public constructor Tree</*0*/ T>(/*0*/ T: [ERROR : Type annotation was missing for parameter T], /*1*/ <no name provided>: Tree<T>, /*2*/ left: [ERROR : Type annotation was missing for parameter left], /*3*/ <no name provided>: Tree<T>, /*4*/ right: [ERROR : Type annotation was missing for parameter right])
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String