Use std::mem::take instead of std::mem::replace with default values

[theherrovn-sys]

Replace std::mem::replace(&mut x, Default::default()) and equivalent patterns (e.g. String::new(), Vec::new(), false) with the more idiomatic std::mem::take(&mut x) across the compiler source.

This improves code readability and aligns with Rust best practices, matching the clippy lint mem_replace_with_default.

Closes #157245.

Changes

File	Change
compiler/rustc_span/src/lib.rs	std::mem::replace(src, String::new()) → std::mem::take(src)
compiler/rustc_middle/src/dep_graph/serialized.rs	mem::replace(&mut local.encoder.data, Vec::new()) → mem::take(&mut local.encoder.data)
compiler/rustc_passes/src/dead.rs	2× mem::replace(&mut self.in_pat, false) → mem::take(&mut self.in_pat)
compiler/rustc_passes/src/check_export.rs	std::mem::replace(&mut self.seen_exportable_in_mod, false) → std::mem::take(...)
compiler/rustc_mir_build/src/check_unsafety.rs	std::mem::replace(&mut self.inside_adt, false) → std::mem::take(...)
compiler/rustc_middle/src/ty/print/pretty.rs	2× std::mem::replace(&mut self.in_value, false) → std::mem::take(...)
compiler/rustc_builtin_macros/src/proc_macro_harness.rs	2× mem::replace(&mut self.in_root, false) → mem::take(&mut self.in_root)

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @mejrs (or someone else) some time within the next two weeks.

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• Owners of files modified in this PR: compiler
• compiler expanded to 73 candidates
• Random selection from 17 candidates

[oli-obk]

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Oli in the name of the mod team