[#401] Omit instructions without location in the debugger snapshots

Description

Problem: there are several issues revealed by 'pexec.tz' contract. First of them: macro handed incorectly, there is no position for expanded instructions, so cursor jumps to the dummy position (at the 0:0). Second: 'APPLY' instruction produce two auxiliary instructions which don't have associated source position either. Also, there is an issue when we jump to a macro line, the cursors goes to dummy position.

Solution: the solution of two first problems is not to make snapshots for instructions without associated source positions and treat them as auxiliary (either generated by the interepreter or added during the contract processing). The last issues is just a bug which can be fixed by attaching appropriate source location.

Based on #438 (closed) commits.

Related issue(s)

Resolves #401 (closed)

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