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).

patch/patches/chrome_browser_browser.patch

@@ -88,7 +88,7 @@ index 4aaba212926f4..e8aadb2c97fe9 100644
  }
  
 diff --git chrome/browser/ui/BUILD.gn chrome/browser/ui/BUILD.gn
-index 977b3222c8f7c..ee71bf3a1a463 100644
+index 977b3222c8f7c..e5d36a4e5921e 100644
 --- chrome/browser/ui/BUILD.gn
 +++ chrome/browser/ui/BUILD.gn
 @@ -8,6 +8,7 @@ import("//build/config/compiler/compiler.gni")
@@ -118,18 +118,21 @@ index 977b3222c8f7c..ee71bf3a1a463 100644
      "//chrome:resources",
      "//chrome:strings",
      "//chrome/app:chrome_dll_resources",
-@@ -699,6 +705,10 @@ static_library("ui") {
+@@ -699,6 +705,13 @@ static_library("ui") {
      deps += [ "//components/plus_addresses/resources:vector_icons" ]
    }
  
 +  if (enable_cef) {
-+    deps += [ "//cef:cef_resources" ]
++    deps += [
++      "//cef:cef_resources",
++      "//cef:make_version_header",
++    ]
 +  }
 +
    # TODO(crbug.com/41437292): Remove this circular dependency.
    # Any circular includes must depend on the target "//chrome/browser:browser_public_dependencies".
    # These are all-platform circular includes.
-@@ -5487,6 +5497,7 @@ static_library("ui") {
+@@ -5487,6 +5500,7 @@ static_library("ui") {
    if (enable_printing) {
      deps += [
        "//components/printing/browser",