Proposal: merge webcomponents.js into index.js and load js in the page head

[wxiaoguang]

Now webcomponents.js is 330Kb and I believe it duplicates some code with index.js

In modern days, I don't see any blocker for putting a JS file in page head, since for more than 99% requests, the file should have already been cached.

@silverwind

[wxiaoguang]

script sizes:

[silverwind]

Yes, dependencies will duplicate into each chunk. Still the script parsing/loading time is shorter in the smaller chunk, not sure if it really matters.

[wxiaoguang]

Then: Merge index.js #34963