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/resource_file_conflict.patch

@@ -0,0 +1,24 @@
+diff --git a/chrome/BUILD.gn b/chrome/BUILD.gn
+index fbcf20c..d2173e2 100644
+--- a/chrome/BUILD.gn
++++ b/chrome/BUILD.gn
+@@ -1656,6 +1656,11 @@ if (is_chrome_branded && !is_android) {
+   }
+ }
+ 
++if (is_electron_gn_build) {
++  group("packed_resources") {
++    public_deps = [ "//electron:packed_resources" ]
++  }
++} else {
+ chrome_paks("packed_resources") {
+   if (is_mac) {
+     output_dir = "$root_gen_dir/repack"
+@@ -1677,6 +1682,7 @@ chrome_paks("packed_resources") {
+     ]
+   }
+ }
++}
+ 
+ repack("browser_tests_pak") {
+   sources = [