FIR: allow fun T.() = ... as an instance of (T) -> ...

It was already done by the previous commit by mistake, but it broke if
there are other value parameters because the type of the first parameter
would be inferred to be same as the type of the receiver.

compiler/fir/tree/src/org/jetbrains/kotlin/fir/diagnostics/ConeSimpleDiagnostic.kt

@@ -27,6 +27,7 @@ enum class DiagnosticKind {
     Java,
     SuperNotAllowed,
     ValueParameterWithNoTypeAnnotation,
+    CannotInferParameterType,
     UnknownCallableKind,
     IllegalProjectionUsage,
     MissingStdlibClass,