fix: allow selecting tables alongside other blocks

[Hbrehman]

Summary

Documents that contain a table could not be selected together with neighbouring blocks, and Ctrl/Cmd+A did not select the whole document.

Rationale

Two prosemirror-tables behaviours trapped the selection inside the table:

1. normalizeSelection treated any TextSelection with one endpoint in a cell and $to.parentOffset === 0 as an accidental intra-table span, and clamped it back to a single cell. That is also the shape of a mouse selection that has just crossed from a table into the next paragraph, and of select-all when the document starts with a table and ends on an empty block.
2. handleMouseDown creates a CellSelection and then refuses to update once the pointer leaves the table (inSameTable).

BlockNote disables TipTap's core extensions, so there was no Mod-a keymap and native select-all was unreliable.

Changes

• Replace stock tableEditing() with a thin wrapper that:
  • keeps cell selection, copy/paste, and table fixing
  • only clamps TextSelections that stay inside the same table
  • converts a cell-drag that leaves the table into a TextSelection spanning the table and the pointer
• Add a Notion-style Mod-a keymap (first press = current block, second = whole document, TextSelection not AllSelection). Table ranges use first/last cell text positions. Whole-doc endpoints that fall inside a table are expanded to the table node's boundaries so Backspace can delete the isolating table instead of only emptying its cells.
• Extract getTableContentRange / getBlockContentRange / getWholeDocTextSelection so setSelection and the keymap share the same table endpoints.

Impact

Cell-to-cell selection inside a table is unchanged. Selections that start outside a table, or that drag out of one, can now include the table and neighbouring blocks. Mod-a is now handled by the editor.

Testing

• Fail-first then passing unit tests in tableCrossBlockSelection.test.ts:
  • setSelection across paragraph+table and table+paragraph
  • TextSelection that leaves a table at parentOffset === 0 is not clamped
  • Mod-a in a table, then again, selects the whole document
  • Mod-a + Backspace clears documents that contain / start with a table
• KeyboardShortcutsExtension.test.ts: Notion-style escalate-and-clear for paragraphs and checklists
• Browser test tableCrossBlockSelection.browser.test.ts for mouse-drag (runs in the Docker e2e suite)
• packages/core unit suite: 778 passed
• Scoped vp lint --type-aware on the changed core files: clean

Screenshots/Video

N/A (selection behaviour; covered by unit tests)

Checklist

• Code follows the project's coding standards.
• Unit tests covering the new feature have been added.
• All existing tests pass.
• The documentation has been updated to reflect the new feature