Move CPDF_Annot and CPDF_AnnotList to their own header.

Review-Url: https://codereview.chromium.org/2163133002
diff --git a/BUILD.gn b/BUILD.gn
index 9c9d865..5426860 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -197,6 +197,10 @@
   sources = [
     "core/fpdfdoc/clines.cpp",
     "core/fpdfdoc/clines.h",
+    "core/fpdfdoc/cpdf_annot.cpp",
+    "core/fpdfdoc/cpdf_annot.h",
+    "core/fpdfdoc/cpdf_annotlist.cpp",
+    "core/fpdfdoc/cpdf_annotlist.h",
     "core/fpdfdoc/cpdf_variabletext.cpp",
     "core/fpdfdoc/cpvt_color.cpp",
     "core/fpdfdoc/cpvt_color.h",
@@ -216,7 +220,6 @@
     "core/fpdfdoc/ctypeset.cpp",
     "core/fpdfdoc/ctypeset.h",
     "core/fpdfdoc/doc_action.cpp",
-    "core/fpdfdoc/doc_annot.cpp",
     "core/fpdfdoc/doc_basic.cpp",
     "core/fpdfdoc/doc_bookmark.cpp",
     "core/fpdfdoc/doc_form.cpp",