Move CPDF_Annot and CPDF_AnnotList to their own header.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 9c9d865c5d56594287a5e4c0bc4326be232d031f..5426860f90fc5a96be9c1370baeb5f6bfd976285 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -197,6 +197,10 @@ static_library("fpdfdoc") {
   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 @@ static_library("fpdfdoc") {
     "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",