perf demangle-rust: Add rustc-demangle C demangler

Imported at commit 80e40f57d99f ("add comment about finding latest
version of code") from:
https://github.com/rust-lang/rustc-demangle/blob/main/crates/native-c/src/demangle.c
https://github.com/rust-lang/rustc-demangle/blob/main/crates/native-c/include/demangle.h

There is discussion of this issue motivating the import in:
rust-lang/rust#60705
https://lore.kernel.org/lkml/[email protected]/

The SPDX lines reflect the dual license Apache-2 or MIT in:
https://github.com/rust-lang/rustc-demangle/blob/main/README.md
Following Migual Ojeda's suggestion comments were added on copyright
and keeping the code in sync with upstream.

The files are renamed as perf supports multiple demanglers and so
demangle as a name would be overloaded.

The work here was done by Ariel Ben-Yehuda <[email protected]> and I
am merely importing it as discussed in the rust-lang issue.

Signed-off-by: Ian Rogers <[email protected]>

Author: captain5050