Code bloat from RawVec::grow_amortized

[glandium]

The change in #72227 made non-PGO builds of Firefox's libxul.so's .text section grow by close to 1MB. libxul.so has a ~89MB section, which makes it a > 1% size increase in a library where about only 16% of the code is rust, which makes it a > 7% (!) increase in size. This comes from the fact that essentially all uses of Vec::push inline this all for some reason, and it's used all across the place.

[tesuji]

@rustbot modify labels: I-heavy T-libs

[rustbot]

Error: Label libs-impl can only be set by Rust team members

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[lcnr]

inling grow_amortized seems to have a noticable performance benefit, so not doing so is probably not desirable, see #78483

Not sure how else we would be able to directly remedy this issue.

[spastorino]

Assigning P-medium as discussed as part of the Prioritization Working Group procedure and removing I-prioritize.