Fix Python multi-line f-strings.

[Yilei (yilei)]

This routes f''' and f""" to dedicates states, which will be closed on matching ''' and """ quotes. It also adds the supported raw-string variant prefixes like rf / rF / ...

This should fix #4601.

[Nicolas Fonteyne (nicolasakf)]

Hi can we please merge this PR. I patched it locally and it solved the problem for me.

[rdejongeviktor]

Any updates on this?

[Jonathan Kingston (jonathanKingston)]

I also hit this and independently reached the same fix as — routing f'''/f""" into dedicated multi-line states — which I now ship as a local grammar override, verified against real tokenization output. One gap worth fixing while you're in there: {{/}} literal braces match the interpolation rule and, in a multi-line state, swallow every following line until a }. Adding [/{{|}}/, 'string'] before the interpolation rule fixes it.