Extend the selected cell range on shift + click.

[dpage]

For pgadmin-org/pgadmin4#8647 ("Cell range selection on shift + click should work").

What changed

• With enableRangeSelection, shift + mousedown on a cell now extends the selected range from the currently selected cell (the anchor) to the clicked cell, in the same way as shift + arrow keys, rather than moving the selection. Repeated shift + clicks keep the same anchor. With range selection disabled, shift + click behaves as a normal click.
• A plain click on the selected cell itself now collapses an extended range back to that cell; previously only clicking a different cell reset it.
• Shift + click whilst a cell editor is open commits the edit and closes the editor before extending the range.
• SelectCellOptions gains an optional extendRange flag.
• lib/ is rebuilt, since pgAdmin installs this fork straight from git.

Test plan

• test/browser/rangeSelection.test.tsx gains tests for shift + click extending the range downwards/rightwards and upwards/leftwards, repeated shift + click keeping the anchor, plain click resetting the range (including on the anchor cell), and shift + click behaving as a normal click when range selection is disabled. They pass in Chromium and Firefox, and four of the five fail without the change.
• Every CI step passes (Biome, typecheck, ESLint, Prettier, bundle, website build, browser tests), apart from the Firefox failure in resizable.test.tsx ("should remeasure flex columns"), which also fails on main.