[Issue 8161] give an error for invalid property functions

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=8161

--- Comment #9 from Nick Treleaven <nick at geany.org> ---
1. The text of this issue mentions -property, but I don't see why we shouldn't
reject the cases it describes *regardless* of the -property switch. (This is
why I removed the switch from the issue title).
2. This is about the *declaration* of nonsensical @property functions, it is
not about optional parentheses in calls.

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