#1255 Implement disallowing specific direct function calls.

Current expression-form check only allows completely disallowing function calls. For cif2uppaal, I need allowing internal user-defined functions.

• Readable by commit.
• The first patch Re-order ExprNoSpecificExprsCheckLevel*.cif checks is only moving lines.

No user-visible changes, as completely disallowing functions has priority and still has the same message.

Not directly relevant for the result, but I used stg (stacked git) here as an experiment, which gives more flexibility in manipulating patch sequences.

Addresses #1255