call _compiler_dispatch for merge_into and copy_into clauses

[sjhewitt]

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1. What GitHub issue is this PR addressing? Make sure that there is an accompanying issue to your PR.

   Fixes #371

2. Fill out the following pre-review checklist:

   • [ ] I am adding a new automated test(s) to verify correctness of my new code
   • [ ] I am adding new logging messages
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   • [ ] I am adding a new dependency

3. Please describe how your code solves the related issue.

This change passes the MergeInto - target, source, on and CopyInto.into values to the compiler

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[sjhewitt]

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