fix: reuse referenced enum component types

[geirsagberg-udir]

Summary

• exclude $ref schemas from inline-enum discovery and property emission
• reuse the declared component enum instead of generating a duplicate property-named enum
• add a regression test for an enum reference whose component and property both map to MessageType

Why

Microsoft.OpenApi exposes the referenced enum values through OpenApiSchemaReference. The emitter therefore classified the reference as an inline enum, emitted both MessageType and MessageType2, and used MessageType2 in the containing record.

This changes generated property types from the property-derived enum name to the referenced component name. That can be source-breaking when consumers regenerate, but it removes an incorrect duplicate public type rather than preserving it behind a compatibility mode.

Verification

• dotnet build --no-restore --configuration Release
• dotnet test --no-build --configuration Release --verbosity normal (272 passed, 1 intentionally skipped)

[nikcio]

@geirsagberg-udir Thanks for this fix