Add initial support for API versioning (see #3836)

- Generated files are now created when running cef_create_projects or
  the new version_manager.py tool. These files are still created in the
  cef/ source tree (same location as before) but Git ignores them due to
  the generated .gitignore file.
- API hashes are committed to Git as a new cef_api_versions.json file.
  This file is used for both code generation and CEF version calculation
  (replacing the previous usage of cef_api_hash.h for this purpose).
  It will be updated by the CEF admin before merging breaking API
  changes upstream.
- As an added benefit to the above, contributor PRs will no longer
  contain generated code that is susceptible to frequent merge conflicts.
- From a code generation perspective, the main difference is that we now
  use versioned structs (e.g. cef_browser_0_t instead of cef_browser_t)
  on the libcef (dll/framework) side. Most of the make_*.py tool changes
  are related to supporting this.
- From the client perspective, you can now define CEF_API_VERSION in the
  project configuration (or get CEF_EXPERIMENTAL by default). This
  define will change the API exposed in CEF’s include/ and include/capi
  header files. All client-side targets including libcef_dll_wrapper
  will need be recompiled when changing this define.
- Examples of the new API-related define usage are provided in
  cef_api_version_test.h, api_version_test_impl.cc and
  api_version_unittest.cc.

To test:
- Run `ceftests --gtest_filter=ApiVersionTest.*`
- Add `cef_api_version=13300` to GN_DEFINES. Re-run configure, build and
  ceftests steps.
- Repeat with 13301, 13302, 13303 (all supported test versions).

tests/cefclient/browser/client_handler.cc

@@ -13,8 +13,8 @@
 
 #include "include/base/cef_callback.h"
 #include "include/cef_browser.h"
-#include "include/cef_command_ids.h"
 #include "include/cef_frame.h"
+#include "include/cef_id_mappers.h"
 #include "include/cef_parser.h"
 #include "include/cef_shared_process_message_builder.h"
 #include "include/cef_ssl_status.h"
@@ -318,6 +318,32 @@ bool IsAllowedToolbarButton(cef_chrome_toolbar_button_type_t button_type) {
 }
 
 bool IsAllowedAppMenuCommandId(int command_id) {
+  // Version-safe static declarations of IDC variables using names from
+  // cef_command_ids.h.
+  CEF_DECLARE_COMMAND_ID(IDC_NEW_WINDOW);
+  CEF_DECLARE_COMMAND_ID(IDC_NEW_INCOGNITO_WINDOW);
+  CEF_DECLARE_COMMAND_ID(IDC_ZOOM_MENU);
+  CEF_DECLARE_COMMAND_ID(IDC_ZOOM_PLUS);
+  CEF_DECLARE_COMMAND_ID(IDC_ZOOM_NORMAL);
+  CEF_DECLARE_COMMAND_ID(IDC_ZOOM_MINUS);
+  CEF_DECLARE_COMMAND_ID(IDC_FULLSCREEN);
+  CEF_DECLARE_COMMAND_ID(IDC_PRINT);
+  CEF_DECLARE_COMMAND_ID(IDC_FIND);
+  CEF_DECLARE_COMMAND_ID(IDC_FIND_NEXT);
+  CEF_DECLARE_COMMAND_ID(IDC_FIND_PREVIOUS);
+  CEF_DECLARE_COMMAND_ID(IDC_MORE_TOOLS_MENU);
+  CEF_DECLARE_COMMAND_ID(IDC_CLEAR_BROWSING_DATA);
+  CEF_DECLARE_COMMAND_ID(IDC_MANAGE_EXTENSIONS);
+  CEF_DECLARE_COMMAND_ID(IDC_PERFORMANCE);
+  CEF_DECLARE_COMMAND_ID(IDC_TASK_MANAGER);
+  CEF_DECLARE_COMMAND_ID(IDC_DEV_TOOLS);
+  CEF_DECLARE_COMMAND_ID(IDC_EDIT_MENU);
+  CEF_DECLARE_COMMAND_ID(IDC_CUT);
+  CEF_DECLARE_COMMAND_ID(IDC_COPY);
+  CEF_DECLARE_COMMAND_ID(IDC_PASTE);
+  CEF_DECLARE_COMMAND_ID(IDC_OPTIONS);
+  CEF_DECLARE_COMMAND_ID(IDC_EXIT);
+
   // Only the commands in this array will be allowed.
   static const int kAllowedCommandIds[] = {
       IDC_NEW_WINDOW,
@@ -361,6 +387,28 @@ bool IsAllowedAppMenuCommandId(int command_id) {
 }
 
 bool IsAllowedContextMenuCommandId(int command_id) {
+  // Version-safe static declarations of IDC variables using names from
+  // cef_command_ids.h.
+  CEF_DECLARE_COMMAND_ID(IDC_CONTENT_CONTEXT_CUSTOM_FIRST);
+  CEF_DECLARE_COMMAND_ID(IDC_CONTENT_CONTEXT_CUSTOM_LAST);
+  CEF_DECLARE_COMMAND_ID(IDC_EXTENSIONS_CONTEXT_CUSTOM_FIRST);
+  CEF_DECLARE_COMMAND_ID(IDC_EXTENSIONS_CONTEXT_CUSTOM_LAST);
+  CEF_DECLARE_COMMAND_ID(IDC_BACK);
+  CEF_DECLARE_COMMAND_ID(IDC_FORWARD);
+  CEF_DECLARE_COMMAND_ID(IDC_RELOAD);
+  CEF_DECLARE_COMMAND_ID(IDC_RELOAD_BYPASSING_CACHE);
+  CEF_DECLARE_COMMAND_ID(IDC_RELOAD_CLEARING_CACHE);
+  CEF_DECLARE_COMMAND_ID(IDC_STOP);
+  CEF_DECLARE_COMMAND_ID(IDC_PRINT);
+  CEF_DECLARE_COMMAND_ID(IDC_CONTENT_CONTEXT_CUT);
+  CEF_DECLARE_COMMAND_ID(IDC_CONTENT_CONTEXT_COPY);
+  CEF_DECLARE_COMMAND_ID(IDC_CONTENT_CONTEXT_PASTE);
+  CEF_DECLARE_COMMAND_ID(IDC_CONTENT_CONTEXT_PASTE_AND_MATCH_STYLE);
+  CEF_DECLARE_COMMAND_ID(IDC_CONTENT_CONTEXT_DELETE);
+  CEF_DECLARE_COMMAND_ID(IDC_CONTENT_CONTEXT_SELECTALL);
+  CEF_DECLARE_COMMAND_ID(IDC_CONTENT_CONTEXT_UNDO);
+  CEF_DECLARE_COMMAND_ID(IDC_CONTENT_CONTEXT_REDO);
+
   // Allow commands added by web content.
   if (command_id >= IDC_CONTENT_CONTEXT_CUSTOM_FIRST &&
       command_id <= IDC_CONTENT_CONTEXT_CUSTOM_LAST) {