[datlechin]

Summary

• Compare Result With… in the result chooser and the View menu opens a comparison window. Left: the result on screen. Right: any other result in the tab, or a pinned result in any query tab on any connection.
• Columns pair by name. A column on one side only is listed, not compared.
• Rows match on Key columns, defaulting to the table's primary key when the result came from one table. No key: whole rows match as a multiset.
• One equality for keys, rows and values: NULL matches NULL, an absent field is not NULL, two spellings of one instant match. A duplicate key stops the comparison and names it.
• Grid follows the Compare & Sync Rows tab: Status and Side columns, only left/right/changed marks, Show filter, counts. VoiceOver says left and right.
• Read-only: reads the rows each result holds, runs no SQL, flags a side cut at the row cap.
• A key change keeps the last answer on screen until the next one lands.
• Compare & Sync row grid: row Copy did nothing, heading clicks offered a sort that did nothing, and a DATE column beside a TIMESTAMP hid the time on the target line. Fixed there and in the new grid.
• ResultSetMenuModelTests and ResultStatusBarLayoutTests updated for the new isComparable and onCompareResultSet parameters.

Test plan

• New suites: ResultColumnPairingTests, ResultComparisonEngineTests, ResultComparisonModelTests, ResultComparisonGridModelTests, GlobalStateSuites/ComparisonGridCopyTests (its Compare & Sync case fails on main).
• UI flow ResultComparisonUITests: run, pin, run again, compare from the chooser, check whole-row counts, key on id, check keyed counts.
• MenuValidationCoverageTests, MainMenuBuilderTests cover the View menu item.

Fixes #3625