Form controls: Space on a focused slider or spin button starts a cell edit

The space a Space press types was dropped while any control was focused, because Space presses
a focused button. A slider or spin button doesn't take Space, so with one focused Space neither
worked the control nor started a cell edit, while every other character did. Now the space is
dropped only for a focused button; on a slider or spin button it reaches the grid like any other
character and starts a cell edit. The control keeps the keyboard, as the control last worked:
Space is a key it doesn't take, exactly like a letter, and letting go on Space alone would make
Space differ from every other printable key.

Test (kittest): space_starts_a_cell_edit_while_a_slider_or_spin_button_is_focused (a cell edit
starts with a space, the control's value is unchanged, Escape cancels, the arrows still step it).
docs/ui-parity.md says so.

docs/ui-parity.md

@@ -69,7 +69,7 @@ this logic, with one undo step.
 | Copy as HTML table for other apps | done (#36, 10-10) |
 | Context menu on cells | 16 items (Cut, Copy, Paste, Paste Special, Insert, Delete, Clear Contents, Filter by value, Sort, New Comment, New Note, Format Cells, Pick From Drop-down List, Define Name, Link). Insert Copied Cells (Insert Cut Cells for whole rows/columns) while the clipboard holds a copy (#21). Show Details on a PivotTable's value, subtotal or grand total cell (`pivot.showDetails`). Missing: Insert Cut Cells for a cell block, paste-option icons, Quick Analysis, Get Data from Table, Show Changes, Smart Lookup |
 | Move and resize charts, pictures and shapes | done (#190, #213): charts, pictures, shapes and slicers select with a frame of eight handles; each handle resizes only its own edges (they never cross), the body moves the object, and the pointer shows a resize or move cursor; Delete or Backspace deletes the selected object and Escape drops the selection; double-click edits a text box, opens Format Chart for a chart. Rotation handle, Shift for proportional resizing, Alt to snap to cells and multi-object selection missing |
-| Form controls: buttons, scroll bars (sliders), spin buttons | done (10-31): Insert › Controls (Button, Slider, Spin Button; Excel has them under Developer › Insert) places one by a drag, or at its default size by a click; a click works a control: drag the thumb, page on the track, click or hold an arrow (a drag or a hold is one undo step), press a button, which runs a macro or a command and asks first in a workbook opened from a file; the control last worked takes the arrows, Page Up and Page Down, Home, End, and Space or Enter (a button gives the keyboard back as soon as the grid takes a key or a right-click); Ctrl or Cmd+click or a right-click selects it to move or resize; its menu has Edit Text, Assign Action, Format Control and Delete. Check boxes, option buttons, list boxes and drop-downs (form controls) are kept from files but not shown |
+| Form controls: buttons, scroll bars (sliders), spin buttons | done (10-31): Insert › Controls (Button, Slider, Spin Button; Excel has them under Developer › Insert) places one by a drag, or at its default size by a click; a click works a control: drag the thumb, page on the track, click or hold an arrow (a drag or a hold is one undo step), press a button, which runs a macro or a command and asks first in a workbook opened from a file; the control last worked takes the arrows, Page Up and Page Down, Home, End, and Space or Enter (a button gives the keyboard back as soon as the grid takes a key or a right-click; Space on a slider or spin button starts a cell edit like any other character); Ctrl or Cmd+click or a right-click selects it to move or resize; its menu has Edit Text, Assign Action, Format Control and Delete. Check boxes, option buttons, list boxes and drop-downs (form controls) are kept from files but not shown |
 | Context menus on row/column headers, sheet tabs, charts, shapes | headers and tabs done; objects partial |
 | Quick Analysis (Ctrl+Q) | missing |
 | Smooth scrolling, scrollbars | done; vertical scrollbar added 10-09 (#73); horizontal scrollbar in the tab bar (60/40 split, drag, track click pages) 10-13 (#176, #840); dragging the handle at the scrollbar's left edge gives the tabs more or less of the bar; each workbook keeps its share while it is open (not saved in the file) |