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/v8_context_snapshot_generator.patch

@@ -0,0 +1,12 @@
+diff --git a/tools/v8_context_snapshot/BUILD.gn b/tools/v8_context_snapshot/BUILD.gn
+index d6691a527f25..000105b86f53 100644
+--- a/tools/v8_context_snapshot/BUILD.gn
++++ b/tools/v8_context_snapshot/BUILD.gn
+@@ -105,6 +105,7 @@ if (use_v8_context_snapshot) {
+     configs += [
+       "//v8:external_startup_data",
+       ":disable_icf",
++      "//electron/build/config:build_time_executable"
+     ]
+   }
+ }