Implement J8 Strings and shopt, for b'' and u''

[andychu]

https://oilshell.zulipchat.com/#narrow/stream/325160-oil-discuss-public/topic/Oil.20Changes.20to.20support.20String.2FData.20language.20Unification

• add \{var} interpolation to $''
• possibly add $"" as a JSON parser, for generating shell code from other languages?
  • then [$"foo", $"bar\n"] becomes a valid ARGV array I guess
  • differences from "": the characters $ and backtick are no longer special
  • possibly add '{var}` as well, for consistency
• double quoted strings can support C-escapes like \x00 and \u{1234}, as long as strict_backslash
• add $"" as a synonym to "", which also makes it consistent with $'' - NO, maintain this assymetry on purpose

[andychu]

Simpler String Unification

https://oilshell.zulipchat.com/#narrow/stream/325160-oil-discuss-public/topic/Simpler.20String.20Unification

• back out changes to $''
• create $"" which is NJ-SQ compatible
• fix up multi-line strings -- only ''' and $"""
  • you don't need either """ or $'''
• write --bs8

[andychu]

Even Simplier Unification with c"" (and existing r'')

https://oilshell.zulipchat.com/#narrow/stream/325160-oil-discuss-public/topic/C.20Prefix.20Idea

TODO:

1. Remove enhancements to $'\n'
2. Rename shopt --set parse_raw_strings -> shopt --set parse_simple_strings or parse_rc_strings
   • make sure that r"" and c'' are syntax errors -- wrong type of quotes
   • although to be honest, I guess you COULD support those, but it would be out of touch with both shell and JSON
3. Implement data language -- JSTR still (not CSTR)
   • read --jstr, instead of read --qsn

[andychu]

Released - https://www.oilshell.org/blog/2024/02/release-0.20.0.html