Unified `validate_{byte,str,raw_str,raw_byte_str}_escape` methods into one method `validate_literal_escape` with a mode argument. This enables simplifying the `match` in `cook_lexer_literal()` and it eliminates 90 lines of repetition :)
Unified `validate_{byte,str,raw_str,raw_byte_str}_escape` methods into one method `validate_literal_escape` with a mode argument.
This enables simplifying the `match` in `cook_lexer_literal()`
and it eliminates 90 lines of repetition :)

graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust