Use an explicit list of "placeholder" tables instead of a magical substring

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When analyzing Metabase queries with references to logical views (aka models), Macaw is passed a query with "sentinel" names in place of actual tables. In order for find-replace to work correctly, [we treat such qualifiers as if they were missing](https://github.com/metabase/macaw/pull/43), so that we can cascade down to the entry qualified by the actual table.

This trick currently relies on Metabase's naming convention, and could have false positives, or break if this convention changes.

A more robust solution would be to take a set of placeholder names to be treated like this. Checking membership in this set should also be faster than searching for substrings too.

Trace the qualifier handling used when analyzing queries with logical views, and locate the current substring-based placeholder check. Replace that convention-dependent check with membership in an explicit set of placeholder names, then verify that cascading still reaches the entry qualified by the actual table and that unrelated qualifiers are unaffected.

Written by the indexing model from the issue text.