Rust lexer updates for language changes.
Rust lexer updates for language changes.

- In strings and character and byte literals,
  ``\uXXXX`` and ``\UXXXXXXXX`` have been replaced with ``\u{X}``.

- ``int`` and ``uint`` are now ``isize`` and ``usize``,
  including their literal form suffixes.

- ``crate`` is a keyword.

- Prelude items are updated.

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