v2.7.3.rc1

• Numerous performance optimizations in JSON.generate and JSON.dump.
• Limit the size of ParserError exception messages, only include up to 32 bytes of the unparseable source.
• Fix json-pure's Object#to_json to accept non state arguments
• Fix multiline comment support in json-pure.
• Fix JSON.parse to no longer mutate the argument encoding when passed an ASCII-8BIT string.
• Fix String#to_json to raise on invalid encoding in json-pure.
• Delete code that was based on CVTUTF.
• Use the pure-Ruby generator on TruffleRuby.
• Fix strict mode in json-pure to not break on Integer.