[graph] Support filtering/collapsing of data flow regions to make huge graphs readable

[utaal]

This may be needed for complex graphs like Frank's epic doop graph.

Various snippets from #1:

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@frankmcsherry

I've been thinking a bit about how to present these, and one thought was: maybe it makes sense to have two nodes for the feedback node, and to not connect them other than visually. This maybe allows the graph to dangle a bit better, and reveals the acyclic definitions.

@comnik

I think this could be a good use case for a touch of interactivity, e.g. draw the nodes somewhat differently to indicate an outgoing / incoming feedback edge, and then highlight the pair when the user hovers on either of the two nodes.

As an experiment, I built an extra script for adding DataScript into the mix. This is intended to be completely opt-in, without changing anything about the current representation.

I also added a hook to re-render the whole thing reactively.

This should give us a low-overhead (no React!) way to experiment with a few more dynamic features, such as highlighting feedback edges.

It would be helpful to have scopes be exported as well, which would allow us to do things such as collapsing / expanding scopes.

[namibj]

I second this, and raise you RSLint's scope-analytics largely-autogenerated dataflow (via differential-dataflow).

I expect this to get worse, considering there are some places where there should be delta-query multijoins instead of chained binary joins.