[rbi] Cleanup handling of how we send parameters to fix issues with inout sending.

[gottesmm]

We previously were not "unsending" inout sending parameters after sending them
so they could not be used again in the caller and could not be forwarded into
other 'inout sending' parameters. While looking at the code I
realized it was pretty obtuse/confusing so I cleaned up the logic and fixed a
few other issues in the process.

Now we follow the following pattern in the non-isolation crossing case:

1. We first require the callee operand.
2. We then merge/require all of the non-explicitly sent parameters.
3. We then through all of the parameters and require/send all of the sending parameters.
4. At the end of processing, we unsend all of the sending parameters that were
   'inout sending' parameters.

In the case of isolation crossing applies we:

1. Require all parameters that are not explicitly marked as sending and then
   send them all at once. We are really just saving a little work by not merging
   them into one large region and then requiring/sending that region once.

2. Then for each sending parameter, we require/send them one by one interleaving
   the requires/sends. This ensures that if a value is passed to different
   explicitly sending parameters, we get an error.

3. Then once we have finished processing results, we perform an undo send on all
   of the 'inout sending' params.

rdar://154440896

[gottesmm]

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