feat(editor): improve latex editing support (#14924)

## Summary
- support converting selected text into inline LaTeX equations
- support turning text blocks into LaTeX equation blocks
- add equation entries to editor toolbars while keeping inline equation
with text formatting actions

## Tests
- yarn tsc -b blocksuite/affine/inlines/latex/tsconfig.json
blocksuite/affine/blocks/note/tsconfig.json
blocksuite/affine/blocks/root/tsconfig.json
blocksuite/affine/rich-text/tsconfig.json
blocksuite/affine/widgets/keyboard-toolbar/tsconfig.json --pretty false
- git diff --check origin/canary...HEAD

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
  * Equation block support with conversion from existing blocks.
  * Inline LaTeX insertion added to the inline formatting toolbar.
* Equation action added to the keyboard toolbar; Equation blocks
searchable via math/equation/latex aliases.

* **Improvements**
* Inline LaTeX editor opens and syncs more reliably; selection/convert
flow preserves distinct LaTeX values when converting in reverse order.

* **Tests**
  * New e2e tests for inline LaTeX conversions and value preservation.

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blocksuite/affine/widgets/keyboard-toolbar/src/config.ts

@@ -222,6 +222,17 @@ const textToolActionItems: KeyboardToolbarActionItem[] = [
       });
     },
   },
+  {
+    name: 'Equation',
+    showWhen: ({ std }) =>
+      std.store.schema.flavourSchemaMap.has('affine:latex'),
+    icon: TeXIcon(),
+    action: ({ std }) => {
+      std.command.exec(updateBlockType, {
+        flavour: 'affine:latex',
+      });
+    },
+  },
   {
     name: 'Quote',
     showWhen: ({ std }) =>