Let a Sequence grow an output as you connect the last one

The Outputs setting is gone. A Sequence now keeps one free output below the
last connected one: nothing plugged in is one output, connecting the spare
grows a new one, unplugging the bottom edge shrinks it back.

It counts the last *connected* port rather than the number of edges, so
unplugging a middle one leaves a gap instead of silently dropping an edge.

Removing the setting also removes a bug it caused. Typing in the Outputs field
did nothing and the arrow keys did nothing, while dragging the value worked:
onInput fires per keystroke, the preview writes into node.params, that emits
'project', and Inspector.refreshValues() sees the node's signature change --
the port list is part of it -- so it rebuilds and destroys the row being typed
in. A drag survives because it keeps receiving globalpointermove on the old
widget. refreshValues() has no focus guard where refreshLive() does; the trap
is still there for the next typed field that changes a node's shape.

Ports that depend on the edges around a node mean derivePorts needs the graph,
not just the params, so resolveDef and portSignature take it too. And a node
whose ports are derived cannot know how many it has from its type, so run is
handed the definition resolved for it.

tests/core/nested-behavior.test.ts

@@ -73,7 +73,7 @@ describe('a behavior used as a node', () => {
     const callee = doubler(fixture);
     const caller = callerOf(fixture, callee, 1);
     const call = caller.graph.nodes.find((n) => n.type === RUN_BEHAVIOR)!;
-    const def = resolveDef(call, behaviorLookup(fixture.project))!;
+    const def = resolveDef(call, caller.graph, behaviorLookup(fixture.project))!;
     expect(def.inputs.map((p) => p.key)).toEqual(['exec', 'in1']);
     expect(def.outputs.map((p) => p.key)).toEqual(['exec', 'out1']);
     // Named after the behavior it runs: a graph of calls is unreadable as a row of "Run behavior".
@@ -214,11 +214,11 @@ describe('a call that cannot do anything says so', () => {
     const start = graphEditor(fixture, callee).addNode(BEHAVIOR_START);
     const caller = makeBehavior(fixture, 'Caller');
     const call = graphEditor(fixture, caller).addNode(RUN_BEHAVIOR, { [BEHAVIOR_PARAM]: callee.id });
-    const signature = () => portSignature(call, behaviorLookup(fixture.project), caller.id);
+    const signature = () => portSignature(call, caller.graph, behaviorLookup(fixture.project), caller.id);
 
     const healthy = signature();
     fixture.stack.execute(new RemoveNodeCommand(callee.id, start.id));
-    expect(resolveDef(call, behaviorLookup(fixture.project))!.label).toBe('Bare');
+    expect(resolveDef(call, caller.graph, behaviorLookup(fixture.project))!.label).toBe('Bare');
     expect(signature()).not.toBe(healthy);
   });