This global was crashing on exit, unsurprising as it contains UNO
services that reference VCL objects.

It turns out that there is already a UNO singleton
framework::ContextChangeEventMultiplexer that effectively contains this
mapping already, so try to hook that up without creating a public API of
it, which is made quite a bit harder by framework's inexplicable
multitude of libraries.

Change-Id: I4baf67b42c630191fa8879d650eeb62520c331a5