fix #35305, need escaping when printing string macro calls

[JeffBezanson]

fix #35305

[vtjnash]

I don't think this actually fixes it, because of #29580, but it is better.

[JeffBezanson]

It looks like that is about printing Regex and SubstitutionString; this is for expressions:

julia> :(r"\\\\")
:(r"\\\\")

But I should change this to only escape backslashes and quotes I think.

[vtjnash]

True, but those happen to be raw"" strings also, like these.

Also, some part of that fix is included in https://github.com/JuliaLang/julia/pull/34111/files#diff-85598a9f3fb3fcced8c43d0472c30888R545

[JeffBezanson]

Oh, nice, we should add that code and use it here.

[JeffBezanson]

Added the commit from #34111. I edited it a bit to not print surrounding "s, since escape_string doesn't.

[mgkuhn]

@JeffBezanson The reason I printed the surrounding " in my original version of escape_raw_string was that I really couldn't think of any reason not to: the entire function really only makes sense if its output is immediately followed by a ", because of the way this encoding specially treats trailing backslashes at the end of the string (expecting the recipient to see that followed by a "). This is different from how escape_string() works, where not only the delimiter is configurable, but also nothing special happens at the end of the string. I'd therefore stay with my original version, as the analogy to escape_string() is not so clear cut.
(The difference in mathematical terms: escape_string() is an isomorphism over string concatenation, whereas escape_string_raw() isn't, because of the case of strings ending in a backslash.)

[JeffBezanson]

That makes sense, but it's easy to add the quotes if you want them, and impossible to remove them if you don't (however unlikely that might be).

[musm]

Looks like this line is unecessary since escape is decremented to 0 by L559

[mgkuhn]

Agreed.