string_lit_as_bytes lint isn't trigged when string contains escaped characters

[upsuper]

I encountered a case where string_lit_as_bytes is not triggered as expected:

let bs = "a byte string\t\n".as_bytes();

If you remove \t\n, then it correctly suggests that it can use byte string literal instead, however, with either \t or \n presents, it doesn't say anything.

I'm testing using Clippy from playground which has version 0.0.212 (2019-10-28 c8e3cfb).

[upsuper]

Probably not too hard to fix, but not trivial either:

rust-clippy/clippy_lints/src/strings.rs

Lines 177 to 180 in f3a207e

	} else if callsite == expanded
	&& lit_content.as_str().chars().all(|c| c.is_ascii())
	&& lit_content.as_str().len() <= MAX_LENGTH_BYTE_STRING_LIT
	&& !args[0].span.from_expansion()

[hellow554]

lit_content.as_str().chars().all(|c| c.is_ascii()) should be lit_content.as_str().is_ascii() while we're at it