This makes a start on clearly factoring the deprecated code of core Cogl
into a deprecated/ directory. Ideally we want to get to the point where
all code here can be re-worked in terms of the public 2.0 api so that it
can be kept indefinitely for cogl 1.x api compatibility without
cluttering the core code base itself. If we can do this then we can
avoid maintaining the Cogl 1.x branches in parallel with master which
would reduce the maintenance effort.
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