Move CPDF_Annot and CPDF_AnnotList to their own header.

BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build_overrides/v8.gni")
 import("//testing/test.gni")
 import("pdfium.gni")
 
 config("pdfium_common_config") {
   cflags = []
@@ skipping 199 matching lines @@
     "core/fpdfdoc/cpvt_sectioninfo.cpp",
     "core/fpdfdoc/cpvt_sectioninfo.h",
     "core/fpdfdoc/cpvt_wordinfo.cpp",
     "core/fpdfdoc/cpvt_wordinfo.h",
     "core/fpdfdoc/csection.cpp",
     "core/fpdfdoc/csection.h",
     "core/fpdfdoc/ctypeset.cpp",
     "core/fpdfdoc/ctypeset.h",
     "core/fpdfdoc/doc_action.cpp",
     "core/fpdfdoc/doc_annot.cpp",
+    "core/fpdfdoc/doc_annot.h",
     "core/fpdfdoc/doc_basic.cpp",
     "core/fpdfdoc/doc_bookmark.cpp",
     "core/fpdfdoc/doc_form.cpp",
     "core/fpdfdoc/doc_formcontrol.cpp",
     "core/fpdfdoc/doc_formfield.cpp",
     "core/fpdfdoc/doc_link.cpp",
     "core/fpdfdoc/doc_metadata.cpp",
     "core/fpdfdoc/doc_ocg.cpp",
     "core/fpdfdoc/doc_tagged.cpp",
     "core/fpdfdoc/doc_utils.cpp",
@@ skipping 1354 matching lines @@
 }
 
 if (pdf_is_standalone) {
   source_set("samples") {
     testonly = true
     deps = [
       "//samples",
     ]
   }
 }