Rolling up some more PRs

Closes #13003 (Make method Vec::remove() public)
Closes #13002 (disallow duplicate methods in trait impls)
Closes #13000 (rustc: test: don't silently ignore bad benches)
Closes #12999 (rustc: buffer the output writer for -Z ast-json[-noexpand].)
Closes #12993 (syntax: Don't parameterize the the pretty printer)
Closes #12990 (`char` reference: s/character/Unicode scalar value/)
Closes #12987 (Move syntax-extension-hexfloat.rs)
Closes #12983 (Fix linkage1 test which fails due to --as-needed)
Closes #12978 (rustc: remove linker_private/linker_private_weak)
Closes #12976 (libsyntax: librustdoc: ignore utf-8 BOM in .rs files)
Closes #12973 (closes #12967 fix [en|de]coding of HashMap<K,V> where K is a numeric type)
Closes #12972 (Add impl IntoStr for ::std::vec_ng::Vec<Ascii>)
Closes #12968 (deny missing docs getopts)
Closes #12965 (Documentation and formatting changes for option.rs.)
Closes #12962 (Relax the memory ordering on the implementation of UnsafeArc)
Closes #12958 (Typo fixes.)
Closes #12950 (Docsprint: Document ops module, primarily Deref.)
Closes #12946 (rustdoc: Implement cross-crate searching)