Go: Fix bad join order in SummarizedParameterNode.gettype

[owen-mc]

Specifically the disjunct for this.getPos() != -1. Running on uber/aresdb, before we had this:

   2403   ~1%    {3} r6 = JOIN `DataFlowUtil::SummarizedParameterNode.getPos/0#dispred#70a2aab4` WITH `DataFlowPrivate::FlowSummaryNode.getSummarizedCallable/0#dispred#e79ea9be` ON FIRST 1 OUTPUT Lhs.1, Lhs.0, Rhs.1
9149774   ~5%    {4}    | JOIN WITH `Types::SignatureType.getParameterType/1#dispred#2c11bb7b_102#join_rhs` ON FIRST 1 OUTPUT Lhs.2, Rhs.1, Lhs.1, Rhs.2
    923   ~9%    {2}    | JOIN WITH `Scopes::Callable.getType/0#dispred#55a0e6a2` ON FIRST 2 OUTPUT Lhs.2, Lhs.3

We add a binding pragma to make it not bind on this.getPos() until necessary. After we have this:

   2403   ~0%    {3} r6 = JOIN `DataFlowUtil::SummarizedParameterNode.getPos/0#dispred#70a2aab4` WITH `DataFlowPrivate::FlowSummaryNode.getSummarizedCallable/0#dispred#e79ea9be` ON FIRST 1 OUTPUT Rhs.1, Lhs.0, Lhs.1
   2373   ~0%    {3}    | JOIN WITH `Scopes::Callable.getType/0#dispred#55a0e6a2` ON FIRST 1 OUTPUT Rhs.1, Lhs.2, Lhs.1
    923   ~9%    {2}    | JOIN WITH `Types::SignatureType.getParameterType/1#dispred#2c11bb7b` ON FIRST 2 OUTPUT Lhs.2, Rhs.2

[owen-mc]

The number of bad join orders identified by DCA goes down from 41 to 11. There is no noticeable effect on performance, so the main effect is making sure this doesn't take a long time on a pathological example.