C++/C#/Shared: Convert the global control-flow library to a shared parameterize module and make it available in C#

[MathiasVP]

This PR does what it says on the (very long) tin 😅

In #149 we added a "shared" global control-flow library. However, at the time I didn't want to introduce a Microsoft-specific shared library into the shared folder because I wasn't aware if this was something we wanted to do. However, I have since learned that we've already done this for our dataflowstack library.

So this PR does two things:

• It converts the "shared" global control-flow library into a properly shared library
• It instantiates the library for C#

This is motivated by an internal ask where global control-flow was needed in C#.

Example usage in C#:

/**
 * @kind path-problem
 */

import csharp as CS
import semmle.code.csharp.interproccontrolflow.ControlFlow
import Flow::PathGraph

module Config implements ControlFlow::ConfigSig {
  predicate isSource(ControlFlow::Node source) {
    // Start at the entry for a method called `A`
    source.(CS::ControlFlow::Nodes::EntryNode).getCallable().hasName("A")
  }

  predicate isSink(ControlFlow::Node sink) {
    // And end at an entry to a method called `B`
    sink.(CS::ControlFlow::Nodes::EntryNode).getEnclosingCallable().hasName("B")
  }
}

module Flow = ControlFlow::Global<Config>;

from Flow::PathNode source, Flow::PathNode sink
where Flow::flowPath(source, sink)
select sink.getNode(), source, sink, ""

Note that I had to import csharp using a qualified import since csharp already exports a module called ControlFlow 😭 Oh well...