Refactor metadata attribute support and add support for [EnumMember]

[andrewlock]

In this PR, you can only choose one source of "metadata attribute" to use for enums:

• [Display]
• [Description]
• [EnumMember] <- New

You can select the source to use by setting the MetadataSource property on the [EnumExtensions] attribute e.g.

[EnumExtensions(MetadataSource = MetadataSource.DisplayAttribute)]
public enum EnumWithDisplayNameInNamespace
{
    First = 0,
    [Display(Name = "2nd")]
    Second = 1,
    Third = 2,
}

Alternatively, you can use MetadataSource.None to choose none of the metadata attributes. In this case, the overloads that take a useMetadataAttributes parameter will not be emitted.

You can set the default metadata source to use for a whole project by setting the EnumGenerator_EnumMetadataSource property in your project:

<PropertyGroup>
  <EnumGenerator_EnumMetadataSource>EnumMemberAttribute</EnumGenerator_EnumMetadataSource>
</PropertyGroup>

The default value is EnumMemberAttribute - TBC, I'm torn between the default being [Display] and [EnumMember]:

• In favor of [Display] and against [EnumMember]: [Display] is already being used by people with the generator, and is often used in a web context for decorating properties as it's a standard DataAnnotations attribute . [EnumMember] is an entirely new attribute, so making that the default would be breaking for literally everyone upgrading the package.
• In favor of [EnumMember] and against [Display]: [EnumMember] is available out of the box, whereas [Display] requires a package for .NET FX and .NET Standard 2.0. Arguably it makes more sense as being the default as it's specifically about serialization.

Fixes #73

[github-actions]

Test Results

    144 files  ±     0      144 suites  ±0   45m 45s ⏱️ + 3m 49s
  6 384 tests + 1 002    6 380 ✅ + 1 002   4 💤 ±0  0 ❌ ±0 
112 400 runs  +17 620  112 328 ✅ +17 620  72 💤 ±0  0 ❌ ±0 

Results for commit 57bd75b. ± Comparison against base commit d3fa4a8.

This pull request removes 12 and adds 1014 tests. Note that renamed tests count towards both.

NetEscapades.EnumGenerators.Tests.EnumGeneratorInterceptorTests ‑ CanGenerateEnumExtensionsWithDescription
NetEscapades.EnumGenerators.Tests.EnumGeneratorInterceptorTests ‑ CanGenerateEnumExtensionsWithDescriptionAndDisplayName
NetEscapades.EnumGenerators.Tests.EnumGeneratorInterceptorTests ‑ CanGenerateEnumExtensionsWithDisplayName
NetEscapades.EnumGenerators.Tests.EnumGeneratorInterceptorTests ‑ CanGenerateEnumExtensionsWithSameDisplayName
NetEscapades.EnumGenerators.Tests.EnumGeneratorInterceptorTests ‑ HandlesStringsWithQuotesAndSlashesInDescription
NetEscapades.EnumGenerators.Tests.EnumGeneratorTests ‑ CanGenerateEnumExtensionsWithDescription
NetEscapades.EnumGenerators.Tests.EnumGeneratorTests ‑ CanGenerateEnumExtensionsWithDescriptionAndDisplayName
NetEscapades.EnumGenerators.Tests.EnumGeneratorTests ‑ CanGenerateEnumExtensionsWithDisplayName
NetEscapades.EnumGenerators.Tests.EnumGeneratorTests ‑ CanGenerateEnumExtensionsWithSameDisplayName
NetEscapades.EnumGenerators.Tests.EnumGeneratorTests ‑ HandlesStringsWithQuotesAndSlashesInDescription
…

NetEscapades.EnumGenerators.IntegrationTests.EnumWithEnumMemberInNamespaceExtensionsTests ‑ GeneratesAsUnderlyingType(value: 3)
NetEscapades.EnumGenerators.IntegrationTests.EnumWithEnumMemberInNamespaceExtensionsTests ‑ GeneratesAsUnderlyingType(value: First)
NetEscapades.EnumGenerators.IntegrationTests.EnumWithEnumMemberInNamespaceExtensionsTests ‑ GeneratesAsUnderlyingType(value: Second)
NetEscapades.EnumGenerators.IntegrationTests.EnumWithEnumMemberInNamespaceExtensionsTests ‑ GeneratesGetNames
NetEscapades.EnumGenerators.IntegrationTests.EnumWithEnumMemberInNamespaceExtensionsTests ‑ GeneratesGetValues
NetEscapades.EnumGenerators.IntegrationTests.EnumWithEnumMemberInNamespaceExtensionsTests ‑ GeneratesGetValuesAsUnderlyingType
NetEscapades.EnumGenerators.IntegrationTests.EnumWithEnumMemberInNamespaceExtensionsTests ‑ GeneratesIsDefined(value: 3)
NetEscapades.EnumGenerators.IntegrationTests.EnumWithEnumMemberInNamespaceExtensionsTests ‑ GeneratesIsDefined(value: First)
NetEscapades.EnumGenerators.IntegrationTests.EnumWithEnumMemberInNamespaceExtensionsTests ‑ GeneratesIsDefined(value: Second)
NetEscapades.EnumGenerators.IntegrationTests.EnumWithEnumMemberInNamespaceExtensionsTests ‑ GeneratesIsDefinedUsingName(name: "-267")
…

♻️ This comment has been updated with latest results.