Fix schemadiff semantics handling

[dbussink]

The problem here is that we store entries in .Tables with their unescaped names, which is entirely safe to do here.

However, we would use sqlparser.String to retrieve them. Now that normally works for table names, unless a table name is a SQL keyword. In that case, it turns into the escaped version with backticks and the whole table can't be found for semantic analysis.

This can happen for example if you name a table Order.

Related Issue(s)

Fixes #16072

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.20%. Comparing base (6def783) to head (0998590).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16073      +/-   ##
==========================================
- Coverage   68.20%   68.20%   -0.01%     
==========================================
  Files        1541     1541              
  Lines      197332   197332              
==========================================
- Hits       134598   134587      -11     
- Misses      62734    62745      +11     

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