Garbage collection

📄️ Introduction

Garbage collection, or GC, can cause jank when it is executed too long and pauses the main Dart code from executing (called "STW", or stop-the-world).

📄️ Within-frame

The following are mainly copied from https://github.com/flutter/engine/pull/36797

📄️ Between-frame

The following are mainly copied from https://github.com/flutter/engine/pull/36834