Auto merge of #8007 - birkenfeld:octal_escapes, r=xFrednet

Add new lint `octal_escapes`

This checks for sequences in strings that would be octal character
escapes in C, but are not supported in Rust.  It suggests either
to use the `\x00` escape, or an equivalent hex escape if the octal
was intended.

Fixes #7981

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changelog: Add new lint [`octal_escapes`], which checks for literals like `"\033[0m"`.