Code generator doesn't preserve individual string quote style

[dhruvmanila]

This is related to the Generator struct.

This is especially true for triple-quoted strings. The Generator will normalize them to single quotes and perform some transformations which may or may not be correct:

• Escape the inner quotes if they match the outer ones
• Preserve the whitespaces (for example, using \n)

Related issues:

• Rules EM102 cause autofix error #6988
• Rule EM102 cause panic assertion failed: self.start_locations.is_empty() #7736
• E731: Preserve multiline string when fixing. #7720

[sanxiyn]

I am interested in working on this.