feat(editor): support user provided role and role schema (#10939)

Let me analyze the key changes in this diff:

1. **Role System Changes**:
- Changed from a fixed enum of roles (`root`, `hub`, `content`) to a more flexible string-based system
- Removed strict role hierarchy validation rules (hub/content/root relationships)
- Added support for role-based matching using `@` prefix (e.g., `@root`, `@content`)

2. **Schema Validation Updates**:
- Added new `_matchFlavourOrRole` method to handle both flavour and role-based matching
- Updated `_validateParent` to consider both roles and flavours when validating parent-child relationships
- Simplified `_validateRole` by removing specific role hierarchy constraints

3. **Block Schema Changes**:
- Updated parent/children references in various block schemas to use the new `@` prefix notation
- Changed parent definitions from `['affine:page']` to `['@root']` in several blocks
- Updated children definitions to use role-based references (e.g., `['@content']`)

4. **Test Updates**:
- Added new test cases for role-based schema validation
- Introduced new test block schemas (`TestRoleBlockSchema`, `TestParagraphBlockSchema`) to verify role-based functionality

This appears to be a significant architectural change that makes the block schema system more flexible by:
1. Moving away from hardcoded role hierarchies
2. Introducing a more dynamic role-based relationship system
3. Supporting both flavour-based and role-based parent-child relationships
4. Using the `@` prefix convention to distinguish role references from flavour references

The changes make the system more extensible while maintaining backward compatibility with existing flavour-based relationships.

blocksuite/affine/blocks/block-surface/src/surface-model.ts

@@ -21,7 +21,7 @@ export const SurfaceBlockSchema = defineBlockSchema({
   metadata: {
     version: 5,
     role: 'hub',
-    parent: ['affine:page'],
+    parent: ['@root'],
     children: [
       'affine:frame',
       'affine:image',