Complex types: Ignore IsOptional fields for structure

[mregen]

fixes #1476
some ModelCompiler versions produce invalid output, for Structure it can be ignored

[codecov]

Codecov Report

Merging #1503 (f542b01) into master (76afe82) will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1503      +/-   ##
==========================================
+ Coverage   51.93%   51.98%   +0.05%     
==========================================
  Files         307      307              
  Lines       58332    58329       -3     
==========================================
+ Hits        30292    30324      +32     
+ Misses      28040    28005      -35     

Impacted Files	Coverage Δ
...es/Opc.Ua.Client.ComplexTypes/ComplexTypeSystem.cs	0.00% <ø> (ø)
...braries/Opc.Ua.Server/Subscription/Subscription.cs	54.48% <0.00%> (+0.11%)	⬆️
...raries/Opc.Ua.Server/Subscription/MonitoredItem.cs	43.78% <0.00%> (+0.30%)	⬆️
...tack/Opc.Ua.Core/Stack/Tcp/TcpTransportListener.cs	72.54% <0.00%> (+0.39%)	⬆️
Libraries/Opc.Ua.Client/Session.cs	61.25% <0.00%> (+0.56%)	⬆️
Stack/Opc.Ua.Core/Types/Utils/ServiceResult.cs	70.09% <0.00%> (+0.93%)	⬆️
Libraries/Opc.Ua.Server/Session/SessionManager.cs	72.41% <0.00%> (+1.03%)	⬆️
Stack/Opc.Ua.Core/Types/BuiltIn/DiagnosticInfo.cs	61.37% <0.00%> (+1.37%)	⬆️
...indings.Https/Stack/Https/HttpsTransportChannel.cs	69.59% <0.00%> (+3.37%)	⬆️
...ack/Opc.Ua.Core/Stack/Transport/AsyncResultBase.cs	66.66% <0.00%> (+5.05%)	⬆️

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[mrsuciu]

Ok