Steps to reproduce

tldr: the goal is to find out how to improve the performance when turning on semantics and scope out work to improve that.

When turning on semantics in Flutter, the app may suffer performance issue due to semantics tree compilation.

We used to only turn on semantics conditionally when needed, but we started to get use cases where we want to turn on by default. For example

1. web platform can't tell whether a assistive technology is running
2. web SEO uses semantics tree to index
3. android app crawl also use accessibilitynodes to crawl the app.

There the things we should do now is to figure out

1. Whether the performance is really bad enough to prevent us from doing that
2. if the answer to 1 is yes, What causes the performance issue
3. if the answer to 1 is yes, What needs to be done to make it run faster.

related issues

Scrolling jank #61193