Move ScopedIPCSupport to mojo/edk/embedder and the mojo::edk namespace.

mojo/edk/embedder/BUILD.gn

Index: mojo/edk/embedder/BUILD.gn
diff --git a/mojo/edk/embedder/BUILD.gn b/mojo/edk/embedder/BUILD.gn
index 529aea3b4913b4db2b140a36abdcd0707185c844..f20fd40230d4b4270364fedf44c28bf55d33f1e4 100644
--- a/mojo/edk/embedder/BUILD.gn
+++ b/mojo/edk/embedder/BUILD.gn
@@ -38,6 +38,8 @@ source_set("embedder") {
     "embedder_internal.h",
     "entrypoints.cc",
     "entrypoints.h",
+    "scoped_ipc_support.cc",
+    "scoped_ipc_support.h",
 
     # Test-only code:
     # TODO(vtl): It's a little unfortunate that these end up in the same