Escape quotes inside identifiers when quoting strings

[barnettben]

The utility extension quotedDatabaseIdentifier wraps a string in double quotes, but doesn't do anything with double quotes already inside the string. This commit escapes existing quotes by repeating them:

- identifier
+ "identifier"

- ident_"with"_quotes
+ "ident_""with""_quotes"

It also adds a couple of simple tests.

• CONTRIBUTING: You have read https://github.com/groue/GRDB.swift/blob/master/CONTRIBUTING.md
• BRANCH: This pull request is submitted against the development branch.
• DOCUMENTATION: Inline documentation has been updated.
• DOCUMENTATION: README.md or another dedicated guide has been updated.
• TESTS: Changes are tested.
• TESTS: The make smokeTest terminal command runs without failure.

[groue]

Thank you @barnettben. Do you have a motivating use case?

[groue]

Note that there exists a previous issue, which was tagged as "Won't fix": #1325

[barnettben]

Hi @groue. I'm sorry, I'd missed that other issue.

This is such an edge case that I'm not keen on pushing for it. I don't think it's a good practice and agree with your assessment in the linked issue that GRDB should not support it.

I made this PR because I'd come across a database that had quotes in a table name and thought it was a quick job to fix. Cheerfully withdrawn!

Oh, I also learned that this is valid 😅:
CREATE TABLE ""("" "");

[groue]

Thanks for taking previous arguments in consideration :-)