Don't embed the attributes in the target dll

[andrewlock]

This stops making it possible to embed the [EnumExtensions] attribute into the target dll by setting "NETESCAPADES_ENUMGENERATORS_EMBED_ATTRIBUTES". This is rarely the right thing to do, and we're already doing the work to ship the attribute in a dedicated dll. This also reduces some of the duplication, removes a config combination to need to test, and opens up the ability to ship "helper" types in the "attributes" dll

[github-actions]

Test Results

   144 files   -     18     144 suites   - 18   2m 18s ⏱️ -50s
 5 372 tests  -  2 090   5 368 ✅  -  2 090   4 💤 ±0  0 ❌ ±0 
92 594 runs   - 36 572  92 522 ✅  - 36 572  72 💤 ±0  0 ❌ ±0 

Results for commit 3f77fa4. ± Comparison against base commit 6ff64d1.

This pull request removes 2090 tests.

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