[datlechin]

Summary

• Set Cells to Value… at the end of Set Value, on the cell's context menu and in Edit > Set Value. Asks for one value and stages it into every target cell, read the way a typed value is. Settings > Keyboard lists it under Data Grid, unbound.
• Targets are the ones the other Set Value items take: the cell selection, else the clicked or focused column on every selected row.
• Cells typing could not edit (read-only or server-owned column, binary column, deleted row) are skipped, and the sheet says how many it sets: "This sets 38 of 40 cells. The others cannot be edited." A column that refuses the value (empty text in a NOT NULL date) keeps its cells and beeps.
• One undo step of ordinary cell edits, so Safe Mode and Preview SQL see them as usual.
• The write is held to the records the sheet was opened over: a load that replaces them while the sheet is up drops it.
• Pasting one value with several cells selected writes it into each of them. A block keeps the anchor paste. Paste stays enabled for this with no focused cell.
• Data file windows keep their own Set Cells to Value: the grid hands it the cells it resolved, and both share one prompt. Its main-menu item moves from Edit > Data to Edit > Set Value, so the menu has one item of that title (MainMenuStructureTests.titlesAreUnique); the column header menu keeps it.
• Data file cleanup commands (Fill Down, Set Cells to Value, Trim Whitespace, Change Case) now change only the selected cells of a split selection, not every row and column between them.
• A paste into many data file cells is one commit and one page refresh, not a page rebuilt per cell.
• Tests changed on purpose: EditSetValueMenuTests (new item, 8 entries), ShortcutUniquenessTests.unboundActionsAreCounted (one more unbound action than main, now 30), ShortcutUniquenessTests.newlyRebindableCommandsAreListable (lists the new action), DataGridRowViewSetValueTests.contextMenuCarriesSetValue.

Docs: TableProApp/docs#74

Test plan

• New DataGridSetCellsToValueTests and GlobalStateSuites/DataGridPasteIntoSelectionTests: targets, skipped cells, the count string, one undo step, a NOT NULL refusal, per-column function reading, rows selected, the record fence, the data file handoff, single-value paste and its menu validation.
• DataFileControllerTests: grid cells reach the data file command; separate cells stay separate; a batch of cell edits is one undo step.
• KeyHandlingTableViewSetValueTests, DataGridRowViewSetValueTests, EditSetValueMenuTests, menu, shortcut, paste and cleared-cell suites rerun.

Fixes #3626