Rollup merge of #129439 - okaneco:vec_string_lossy, r=Noratrieb

Implement feature `string_from_utf8_lossy_owned` for lossy conversion from `Vec<u8>` to `String` methods

Accepted ACP: rust-lang/libs-team#116
Tracking issue: #129436

Implement feature for lossily converting from `Vec<u8>` to `String`
- Add `String::from_utf8_lossy_owned`
- Add `FromUtf8Error::into_utf8_lossy`

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Related to #64727, but unsure whether to mark it "fixed" by this PR.
That issue partly asks for in-place replacement of the original allocation. We fulfill the other half of that request with these functions.

closes #64727