build: move libcc patches to electron repo (#14104)

In the GN build, libchromiumcontent is no longer a distinct library, but
merely a container for a set of scripts and patches. Maintaining those
patches in a separate repository is tedious and error-prone, so merge
them into the main repo.

Once this is merged and GN is the default way to build Electron, the
libchromiumcontent repository can be archived.

patches/common/chromium/allow_webview_file_url.patch

@@ -0,0 +1,13 @@
+diff --git a/content/browser/loader/resource_dispatcher_host_impl.cc b/content/browser/loader/resource_dispatcher_host_impl.cc
+index 0c57d20..0916ed0 100644
+--- a/content/browser/loader/resource_dispatcher_host_impl.cc
++++ b/content/browser/loader/resource_dispatcher_host_impl.cc
+@@ -1870,6 +1870,8 @@ void ResourceDispatcherHostImpl::BeginNavigationRequest(
+       !policy->IsWebSafeScheme(info.common_params.url.scheme()) &&
+       !is_external_protocol;
+ 
++  non_web_url_in_guest = false;
++
+   if (is_shutdown_ || non_web_url_in_guest ||
+       (delegate_ && !delegate_->ShouldBeginRequest(
+           info.common_params.method,