Add documentation for keyboard shortcut selecting text across multiple blocks (#43164)

---------

Co-authored-by: Aaron Robertshaw <60436221+aaronrobertshaw@users.noreply.github.com>

Author: bengreeley

docs/explanations/faq.md

@@ -219,6 +219,11 @@ This is the canonical list of keyboard shortcuts:
 			<td><kbd>Esc</kbd></td>
 			<td><kbd>Esc</kbd></td>
 		</tr>
+		<tr>
+			<td>Select text across multiple blocks.</td>
+			<td></td>
+			<td><kbd>Shift</kbd>+<kbd>Arrow (⇦, ⇧, ⇨, ⇩)</kbd></td>
+		</tr>
 	</tbody>
 </table>
 

packages/block-editor/src/components/keyboard-shortcuts/index.js

@@ -93,6 +93,16 @@ function KeyboardShortcutsRegister() {
 			},
 		} );
 
+		registerShortcut( {
+			name: 'core/block-editor/multi-text-selection',
+			category: 'selection',
+			description: __( 'Select text across multiple blocks.' ),
+			keyCombination: {
+				modifier: 'shift',
+				character: 'arrow',
+			},
+		} );
+
 		registerShortcut( {
 			name: 'core/block-editor/focus-toolbar',
 			category: 'global',

packages/edit-post/src/components/keyboard-shortcut-help-modal/test/__snapshots__/index.js.snap

@@ -272,6 +272,35 @@ exports[`KeyboardShortcutHelpModal should match snapshot when the modal is activ
               </kbd>
             </div>
           </li>
+          <li
+            class="edit-post-keyboard-shortcut-help-modal__shortcut"
+          >
+            <div
+              class="edit-post-keyboard-shortcut-help-modal__shortcut-description"
+            >
+              Select text across multiple blocks.
+            </div>
+            <div
+              class="edit-post-keyboard-shortcut-help-modal__shortcut-term"
+            >
+              <kbd
+                aria-label="Shift + Arrow"
+                class="edit-post-keyboard-shortcut-help-modal__shortcut-key-combination"
+              >
+                <kbd
+                  class="edit-post-keyboard-shortcut-help-modal__shortcut-key"
+                >
+                  Shift
+                </kbd>
+                +
+                <kbd
+                  class="edit-post-keyboard-shortcut-help-modal__shortcut-key"
+                >
+                  Arrow
+                </kbd>
+              </kbd>
+            </div>
+          </li>
         </ul>
       </section>
       <section