Map GDS call is passing a FactorizedTable instead of a schema

[semihsalihoglu-uw]

I was in the following situation. I'm parallelizing the writes of the GDS outputs. In this case, each thread needs to create a local copy of an FTable. The current PlanMapper::mapGDSCall passes an actual FTable instead of TableSchema down to the operators (putting this in the GDSCallSharedState). This left me in a situation where I wanted to copy or clone the FTable but there is no such function.

Having talked to @acquamarin apparently normally the frontend passes just the schema and each operator that wants to do parallel writes, e.g., ResultCollector, use this schema to create its local copy with a line like this (see ResultCollector::initLocalStateInternal for an example):

    localTable = std::make_unique<FactorizedTable>(context->clientContext->getMemoryManager(),
        info.tableSchema.copy());

So maybe we should follow this style also in GDSCall. Or we can add a clone function to FTable and pass in FTable in other places too. Regardless, let's be consistent everywhere for code readability.