Add conformance test for `@final` combined with `@property`

[samwgoldman]

The language of the typing spec indicates that the @final decorator may be used with properties:

The method decorator version may be used with all of instance methods, class methods, static methods, and properties.

I noticed this case while working on Pyre. I observed that Mypy and Pyright also differ in behavior, so it seemed like a good conformance test to add.

See discussion here: https://discuss.python.org/t/proposal-allow-chaining-final-decorator-when-previous-decorators-return-a-non-function/78918

I also added an example to the spec itself. I think it's a practical example, but also happy to remove it as well, since the existing content makes it pretty clear that the example should be allowed.

[ghost]

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[erictraut]

Thanks for reporting this and adding the conformance test. FYI, I've filed the following bug in the pyright issue tracker: https://github.com/microsoft/pyright/issues/9795.

[samwgoldman]

Thanks for the guidance!

[hauntsaninja]

I guess always a risk changing a pyright conformant value, because odds are 50/50 that Eric will have fixed it before the PR is merged :-)