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).

tools/make_libcef_dll_dylib_impl.py

@@ -10,7 +10,8 @@ import os
 # Other headers that export C API functions.
 OTHER_HEADERS = [
     'cef_api_hash.h',
-    'cef_version.h',
+    'cef_id_mappers.h',
+    'cef_version_info.h',
     'internal/cef_dump_without_crashing_internal.h',
     'internal/cef_logging_internal.h',
     'internal/cef_string_list.h',
@@ -37,12 +38,11 @@ def make_libcef_dll_dylib_impl_parts(name, retval, args):
 
   declare = 'decltype(&%s) %s;\n' % (name, name)
 
-  init = '  INIT_ENTRY(%s);' % name
+  init = 'INIT_ENTRY(%s);\n' % name
 
   impl = """NO_SANITIZE("cfi-icall") %s %s(%s) {
   %sg_libcef_pointers.%s(%s);
 }
-
 """ % (retval, name, ', '.join(args), 'return '
        if retval != 'void' else '', name, arg_names)
 
@@ -70,9 +70,10 @@ def make_libcef_dll_dylib_impl(header):
   # Include required headers for global functions.
   for func in header.get_funcs():
     declare, init, impl = make_libcef_dll_dylib_impl_func(func)
-    ptr_declare += declare
-    ptr_init += init
-    ptr_impl += impl
+    pre, post = get_version_surround(func)
+    ptr_declare += pre + declare + post
+    ptr_init += pre + init + post
+    ptr_impl += pre + impl + post + '\n'
 
     filename = func.get_file_name()
     if not filename in filenames:
@@ -85,9 +86,13 @@ def make_libcef_dll_dylib_impl(header):
     funcs = cls.get_static_funcs()
     for func in funcs:
       declare, init, impl = make_libcef_dll_dylib_impl_func(func)
-      ptr_declare += declare
-      ptr_init += init
-      ptr_impl += impl
+      pre1, post1 = get_version_surround(func)
+      pre2, post2 = get_version_surround(cls)
+      pre = pre1 + pre2
+      post = post1 + post2
+      ptr_declare += pre + declare + post
+      ptr_init += pre + init + post
+      ptr_impl += pre + impl + post + '\n'
 
     if len(funcs) > 0:
       filename = cls.get_file_name()
@@ -106,7 +111,7 @@ def make_libcef_dll_dylib_impl(header):
           func['name'], func['retval'], func['args'])
       ptr_declare += declare
       ptr_init += init
-      ptr_impl += impl
+      ptr_impl += impl + '\n'
 
     includes.append('#include "include/%s"' % other)
 
@@ -202,7 +207,9 @@ if __name__ == "__main__":
   # Create the header object. Should match the logic in translator.py.
   header = obj_header()
   header.set_root_directory(cpp_header_dir)
-  excluded_files = ['cef_api_hash.h', 'cef_application_mac.h', 'cef_version.h']
+  excluded_files = [
+      'cef_api_hash.h', 'cef_application_mac.h', 'cef_version_info.h'
+  ]
   header.add_directory(cpp_header_dir, excluded_files)
   header.add_directory(os.path.join(cpp_header_dir, 'test'))
   header.add_directory(os.path.join(cpp_header_dir, 'views'))