Rollup merge of #103117 - joshtriplett:use-is-terminal, r=eholk

Rollup merge of #103117 - joshtriplett:use-is-terminal, r=eholk

Use `IsTerminal` in place of `atty`

In any crate that can use nightly features, use `IsTerminal` rather than
`atty`:

- Use `IsTerminal` in `rustc_errors`
- Use `IsTerminal` in `rustc_driver`
- Use `IsTerminal` in `rustc_log`
- Use `IsTerminal` in `librustdoc`