Add support for retrieving multiple enum values from the `UpdateMethod` property of the `UpdateRestrictions` annotation

[irvinesunday]

We need to add support for retrieving multiple enum values from the UpdateMethod property value of UpdateRestrictions annotations.

example:

<Annotations Target="microsoft.graph.customClaimsPolicy/claims">
  <Annotation Term="Org.OData.Capabilities.V1.UpdateRestrictions">
    <Record>
      <PropertyValue Property="UpdateMethod">
        <Collection>
          <EnumMember>Org.OData.Capabilities.V1.HttpMethod/PUT Org.OData.Capabilities.V1.HttpMethod/PATCH</EnumMember>
        </Collection>              
      </PropertyValue>
    </Record>
  </Annotation>
</Annotations>

[baywet]

Dumping some of the conversation elements:

We'll need to update these blocks (multiple places) not to be if/else, but if first condition, if second condition.

OpenAPI.NET.OData/src/Microsoft.OpenApi.OData.Reader/PathItem/EntityPathItemHandler.cs

Line 37 in 46c1490

UpdateRestrictionsType updateRestrictions = Context.Model.GetRecord<UpdateRestrictionsType>(TargetPath, CapabilitiesConstants.UpdateRestrictions);

The enum above needs to be flaggable

OpenAPI.NET.OData/src/Microsoft.OpenApi.OData.Reader/Vocabulary/Capabilities/UpdateRestrictionsType.cs

Line 161 in 46c1490

UpdateMethod = record.GetEnum<HttpMethod>("UpdateMethod");

so it matches its vocab definition
https://github.com/oasis-tcs/odata-vocabularies/blob/a7850482cc83488d37c66c4e907f6a94406e1d05/vocabularies/Org.OData.Capabilities.V1.xml#L764C23-L764C33

And we might have to update the GetEnumMember helper so it supports flags enums.

OpenAPI.NET.OData/src/Microsoft.OpenApi.OData.Reader/Edm/RecordExpressionExtensions.cs

Line 96 in 46c1490

public static T? GetEnum<T>(this IEdmRecordExpression record, string propertyName)

[baywet]

Another aspect to consider when emitting the multiple operations is the operation id:

• they should not collide, including with POST when present
• PUT should be Update by default, New when POST is absent AND PATCH is present.
• PATCH should be Update
• POST should be New

This leaves a question of what should the Id be for PUT when all of POST/PATCH/PUT are present?