gh-87092: create a 'jump target label' abstraction so that the compiler's codegen stage does not work directly with basic blocks (GH-95398)

Author: iritkatriel

Misc/NEWS.d/next/Core and Builtins/2022-07-28-19-07-06.gh-issue-87092.73IPS1.rst

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+Create a 'jump target label' abstraction in the compiler so that the compiler's codegen stage does not work directly with basic blocks. This prepares the code for changes to the underlying CFG generation mechanism.