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).

libcef_dll/libcef_dll2.cc

@@ -4,15 +4,24 @@
 //
 
 #include <cstddef>
+#include <map>
+#include <string_view>
 
-#include "include/base/cef_build.h"
-#include "include/cef_api_hash.h"
-#include "include/cef_version.h"
+#include "base/logging.h"
+#include "base/no_destructor.h"
+#include "cef/include/base/cef_build.h"
+#include "cef/include/cef_api_hash.h"
+#include "cef/include/cef_id_mappers.h"
+#include "cef/include/cef_version_info.h"
 
 #if defined(OS_WIN)
-#include "include/internal/cef_win.h"
+#include "cef/include/internal/cef_win.h"
 #endif
 
+namespace {
+int g_version = -1;
+}
+
 CEF_EXPORT int cef_version_info(int entry) {
   switch (entry) {
     case 0:
@@ -36,19 +45,117 @@ CEF_EXPORT int cef_version_info(int entry) {
   }
 }
 
-CEF_EXPORT const char* cef_api_hash(int entry) {
+#include "cef/libcef_dll/cef_api_versions.inc"
+
+CEF_EXPORT const char* cef_api_hash(int version, int entry) {
+  static const ApiVersionHash* hash = nullptr;
+
+  // Initialize on the first successful lookup.
+  if (!hash) {
+    for (size_t i = 0; i < kApiVersionHashesSize; ++i) {
+      if (version == kApiVersionHashes[i].version) {
+        hash = &kApiVersionHashes[i];
+        break;
+      }
+    }
+
+    if (hash) {
+      g_version = version;
+    }
+  }
+
+  if (!hash) {
+    LOG(ERROR) << "Request for unsupported CEF API version " << version;
+    return nullptr;
+  }
+
+  if (version != g_version) {
+    LOG(ERROR) << "CEF API version cannot be configured multiple times";
+    return nullptr;
+  }
+
   switch (entry) {
     case 0:
-      return CEF_API_HASH_PLATFORM;
+      return hash->platform;
     case 1:
-      return CEF_API_HASH_UNIVERSAL;
+      return hash->universal;
     case 2:
       return CEF_COMMIT_HASH;
     default:
-      return NULL;
+      return nullptr;
   }
 }
 
+CEF_EXPORT int cef_api_version() {
+  return g_version;
+}
+
+#include "cef/libcef_dll/cef_pack_resources.inc"
+
+CEF_EXPORT int cef_id_for_pack_resource_name(const char* name) {
+  static base::NoDestructor<std::map<std::string_view, int>> string_to_id_map;
+
+  // Initialize on the first call.
+  if (string_to_id_map->empty()) {
+    for (size_t i = 0; i < kIdNamesPackResourcesSize; ++i) {
+      (*string_to_id_map)[kIdNamesPackResources[i].name] =
+          kIdNamesPackResources[i].id;
+    }
+  }
+
+  const auto& it = string_to_id_map->find(name);
+  if (it != string_to_id_map->end()) {
+    return it->second;
+  }
+
+  LOG(WARNING) << __func__ << " called with unsupported value " << name;
+  return -1;
+}
+
+#include "cef/libcef_dll/cef_pack_strings.inc"
+
+CEF_EXPORT int cef_id_for_pack_string_name(const char* name) {
+  static base::NoDestructor<std::map<std::string_view, int>> string_to_id_map;
+
+  // Initialize on the first call.
+  if (string_to_id_map->empty()) {
+    for (size_t i = 0; i < kIdNamesPackStringsSize; ++i) {
+      (*string_to_id_map)[kIdNamesPackStrings[i].name] =
+          kIdNamesPackStrings[i].id;
+    }
+  }
+
+  const auto& it = string_to_id_map->find(name);
+  if (it != string_to_id_map->end()) {
+    return it->second;
+  }
+
+  LOG(WARNING) << __func__ << " called with unsupported value " << name;
+  return -1;
+}
+
+#include "cef/libcef_dll/cef_command_ids.inc"
+
+CEF_EXPORT int cef_id_for_command_id_name(const char* name) {
+  static base::NoDestructor<std::map<std::string_view, int>> string_to_id_map;
+
+  // Initialize on the first call.
+  if (string_to_id_map->empty()) {
+    for (size_t i = 0; i < kIdNamesCommandIdsSize; ++i) {
+      (*string_to_id_map)[kIdNamesCommandIds[i].name] =
+          kIdNamesCommandIds[i].id;
+    }
+  }
+
+  const auto& it = string_to_id_map->find(name);
+  if (it != string_to_id_map->end()) {
+    return it->second;
+  }
+
+  LOG(WARNING) << __func__ << " called with unsupported value " << name;
+  return -1;
+}
+
 #if defined(OS_WIN)
 
 #if defined(ARCH_CPU_32_BITS)