Don't duplicate the extern providers once for each crate

[bjorn3]

This should give a small perf improvement for small crates by avoiding a memcpy of a pretty big struct for each loaded crate. In addition would be useful for replacing the sequential CrateNum everywhere with the hash based StableCrateId introduced in #81635, which would allow avoiding remapping of CrateNum's when loading crate metadata. While this PR is not strictly needed for that, it is necessary to prevent a performance loss due to it.

I think this duplication was done in #40008 (which introduced the query system) to make it possible to compile multiple crates in a single session in the future. I think this is unlikely to be implemented any time soon. In addition this PR can easily be reverted if necessary to implement this.

[rust-highfive]

r? @petrochenkov

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[bjorn3]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit cd7a011 with merge 47f4b9cd95f9b17537af3b251c2e5b97369c3acf...

[bors]

☀️ Try build successful - checks-actions
Build commit: 47f4b9cd95f9b17537af3b251c2e5b97369c3acf (47f4b9cd95f9b17537af3b251c2e5b97369c3acf)

[rust-timer]

Queued 47f4b9cd95f9b17537af3b251c2e5b97369c3acf with parent 3aedcf0, future comparison URL.

[rust-timer]

Finished benchmarking try commit (47f4b9cd95f9b17537af3b251c2e5b97369c3acf): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf

[petrochenkov]

@bors r+

[bors]

📌 Commit cd7a011 has been approved by petrochenkov

[bors]

⌛ Testing commit cd7a011 with merge a0e229a...

[bors]

☀️ Test successful - checks-actions
Approved by: petrochenkov
Pushing a0e229a to master...