fix: pass --extern-html-root-takes-precedence in addition to --extern-html-root-url on rustdoc invocation

[motorailgun]

The fix mentioned in tests (rust-lang/rust#82776) is already merged upstream, so I believe this works now.

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[weihanglo]

I feel like this is understood backwards here.

rust-lang/rust#82776 was the reason we disabled the test. See #9824

(I personally don't really have the context of the back-and-forth of these flags though)

View changes since the review

[motorailgun]

Oh, sorry I didn't dig deeper into git blame. As per my understanding (reading through discussions and histories), --extern-html-root-takes-precedence preserves original behavior that cargo has/had been expecting, so I believe passing this to rustdoc would solve this breakage...?

[weihanglo]

Not really. rust-lang/rust#82776 added --extern-html-root-takes-precedence and

rust-lang/rust#82776 (comment)

The flag here (--extern-html-root-takes-precedence) might be fine, I was just trying to understand what this was being added for. If it was for cargo, then I think this PR wasn't what we really needed. But if it was added for other users, then that would be good to know those use cases.