Moved LayoutInflater#mContext to dark grey list

In LayoutInflater, moved the member mContext to dark grey list of APIs,
disabling access for apps targeting Q. Developers should use the provided
getter getContext to retrieve the context or the method cloneInContext to
create a LayoutInflater copy with a different context. Both methods are
available since API 1.

Bug: 117519957
Test: android.view.cts.LayoutInflaterTest
Change-Id: Id86969dddb14fafd76fda1b0a97c7f8fc09aca3e