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We add node/tests.SchemaTestAll to simplify this task, meaning we don't
need to duplicate all test func declarations in node/bindnode.
SchemaTestAll is also flexible enough to allow running multiple
sub-tests per schema test in the future.

There were two remaining places in node/tests that still weren't using
ipld.DeepEqual, so fix those.

Finally, bindnode needed a couple of changes to fully support
ipld.DeepEqual. Most notable is iteration over maps, which required a
bit of a refactor to keep ordered keys.

Along with a generic Engine interface, so that they can be reused for
other ipld.Node implementations, such as bindnode.

node/bindnode will start using these in a follow-up commit, since this
one is large enough as is.

Tested that all three forms of testing schema/gen/go still work:

	go test

	CGO_ENABLED=0 go test

	go test -tags=skipgenbehavtests