Issue #7151 : Load Execute SQL script from a file and restyle the dialog

[mattcasters]

What

Execute SQL script can load the script from a VFS SQL file instead of only storing it in the pipeline XML (#7151). The dialog is reorganized onto three tabs.

Changes

• Add sql_from_file (same pattern as Table Input / Database Join): when set, SQL is read from that path at transform init; variables in the path are resolved; the editor is a read-only preview.
• Restyle the dialog with GuiCompositeWidgets tabs:
  • General: connection and insert/update/delete/read stats fields
  • SQL: filename, script editor, execute for each row, single statement, variable substitution, quote strings
  • Parameters: bind parameters and the argument table (Get Fields remains on the button bar)
• Unit tests for getEffectiveSql, load/save of sqlFromFile, and disabled GUI widgets
• Integration test 0019-execute-sqlscript-sql-file (inline SQL is a dummy SELECT 1; the file is the source of truth)
• User-manual page updated with screenshots of the three tabs

Fixes #7151