Disable missing-ref for types with `getproperty`

[pfitzseb]

I saw the same thing today with

function f(df)
    println(f.my_column[1])
end

Originally posted by @hhaensel in #4149

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That deserves its own issue, because DataFrames have dynamically computed properties. The correct way to handle this is to never display missing-ref diagnostics for objects whose type we can determine and which have getproperty defined for them.