Module level let detupling

[Jand42]

    let a, b = 1, 2

in a module currently fails with Method name not found in JavaScript compilation: (patternInput@12-27 : unit -> (System.Int32 * System.Int32)).

This was a limitation in WebSharper 3 because of unsuitable behavior of F# compiler around module-level pattern lets with ReflectedDefinion (see #346), but should not be an issue with WebSharper 4 (using FCS).

The bug is caused by ignoring compiler generated methods of F# types. F# module, record and union properties, union case constructor methods and so on are treated specially, but patternInput here is also a module property is not exposed as a SourceMember definition by FCS.