Stabilize Option::get_or_insert_default

[coolreader18]

FCP completed in #82901.

Stabilized API:

impl<T> Option<T> {
    pub fn get_or_insert_default(&mut self) -> &mut T where T: Default;
}

[rustbot]

r? @Amanieu

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[rust-log-analyzer]

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#16 2.871 Building wheels for collected packages: reuse
#16 2.872   Building wheel for reuse (pyproject.toml): started
#16 3.121   Building wheel for reuse (pyproject.toml): finished with status 'done'
#16 3.122   Created wheel for reuse: filename=reuse-4.0.3-cp310-cp310-manylinux_2_35_x86_64.whl size=132715 sha256=dfa09868353292d98f811d3efdb0d54d07389e808efc71d68e3b93c514bf8bec
#16 3.122   Stored in directory: /tmp/pip-ephem-wheel-cache-lmni8d8j/wheels/3d/8d/0a/e0fc6aba4494b28a967ab5eaf951c121d9c677958714e34532
#16 3.125 Installing collected packages: boolean-py, binaryornot, tomlkit, reuse, python-debian, markupsafe, license-expression, jinja2, chardet, attrs
#16 3.519 Successfully installed attrs-23.2.0 binaryornot-0.4.4 boolean-py-4.0 chardet-5.2.0 jinja2-3.1.4 license-expression-30.3.0 markupsafe-2.1.5 python-debian-0.1.49 reuse-4.0.3 tomlkit-0.13.0
#16 3.519 WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv
#16 DONE 3.6s

[workingjubilee]

rustc_session uses it

[tguichaoua]

Isn't a duplicate of #129087?

[coolreader18]

Ah, shoot, you're right, I didn't see that when I searched.