Fix python-fill-paragraph problems on filling strings (bug#62142)

Fix python-fill-paragraph problems on filling strings (bug#62142)

* lisp/progmodes/python.el (python-syntax--context-compiler-macro)
(python-syntax-context): Add single-quoted-string and
triple-quoted-string as TYPE argument.
(python-info-triple-quoted-string-p): New helper function.
(python-fill-paragraph)
(python-fill-string): Use it.
* test/lisp/progmodes/python-tests.el (python-syntax-context-1)
(python-fill-paragraph-single-quoted-string-1)
(python-fill-paragraph-single-quoted-string-2)
(python-fill-paragraph-triple-quoted-string-1)
(python-info-triple-quoted-string-p-1)
(python-info-triple-quoted-string-p-2)
(python-info-triple-quoted-string-p-3): New tests.