Until now, the only usage of ruleset layers was where there is both a
ruleset specific and non-ruleset-specific layer present. The matching
code was making assumptions about this.
As I tried to add a new playfield layer which breaks this assumption,
non-ruleset-specifc components were not being displayed in the toolbox.
This turned out to be due to a `target` of `null` being provided due to
the weird `getTarget` matching (that happened to *just* do what we
wanted previously due to the equals implementation, but only because
there was a container without the ruleset present in the available
targets).
I've changed this to be a more appropriate lookup method, where the
target for dependency sourcing is provided separately from the ruleset
filter.
Dean Herbert
5bd06832d0