Add backslashed single quotes to grammar

[kislikjeka98]

It breaks if use single quoted string with backslash escaped single quote, for example 'Author's name'.
But mysql and postgres accept it
https://dev.mysql.com/doc/refman/8.4/en/string-literals.html
https://www.postgresql.org/docs/current/sql-syntax-lexical.html

I think it can be fixed by changing single_quote grammar to this

{
	"_single_quote_string": {
		"type": "SEQ",
		"members": [
			{
				"type": "PATTERN",
				"value": "([uU]&)?'(''|[^'\\]|\\.)*'"
			},
			{
				"type": "REPEAT",
				"content": {
					"type": "PATTERN",
					"value": "'(''|[^'\\]|\\.)*'"
				}
			}
		]
	}
}

[matthias-Q]

This change is not enough, unfortunately. I have tested it and it breaks some tests (COPY FROM STDIN, because there a backslash can be set as an escape char)

[kislikjeka98]

In my mind COMMENT used more frequiently than copy statements with EXCAPE ''
But i will think what to with this case

[matthias-Q]

Correct, but the parser work in all cases. I would really not like to remove functionality.

I did not had the time to look deeper into that issue.