Support stage-4 ergonomic brand checks for private fields

[sosukesuzuki]

Describe the feature

Support ergonomic brand checks proposal that is now Stage-4.

Babel plugin or link to the feature description

Now Babel 7.15 supports it in default.

Additional context

Nothing

[kdy1]

Thanks for the info!

[HiZhaoxiaoyang]

开始还以为shock wave component又卷土重来了。