Problem

Currently the Flutter engine "streams" each semantic node update and custom action update individually to the embedder. A semantic node update can refer to a custom action update, so the ordering of these updates is important or it can cause crashes (see #103808 and flutter/engine#35792).

Fix

These ordering requirements are subtle and error prone. We can simplify the embedder API by introducing a new callback that provides the complete batch of semantic updates.

Steps

• Introduce a new embedder API: [Embedder API] Introduce new semantics update callback and migrate Windows engine#37129
• Migrate Windows to new embedder API: [Embedder API] Introduce new semantics update callback and migrate Windows engine#37129
• Migrate macOS to new embedder API: [macOS] Move to new update semantics embedder API engine#37404
• Migrate Linux to new embedder API: [Linux] Migrate to the new update semantics embedder API #132517