Implement code generation for direct port calls

[bocchino]

Implement the code generation for nasa/fprime#3986.

• Add a compilation switch FW_DIRECT_PORT_CALLS.
• When the switch is set to zero, use the standard F Prime ports. This approach can support unit testing.
• When the switch is set to nonzero, use direct port calls. Move the implementation of port invocation from the component module to the topology module, and use the topology model to generate a switch statement that directly calls the receiver functions in the target components.

This issue includes the FPP unit tests.