Preserve empty string enum values during generation

[AayushP123]

Summary

Retains empty string values when building enum CodeDOM options. Distinguishes an explicitly empty serialization name from an unset one, and verifies the Go writer emits and parses the empty wire value.

This allows schemas with values such as M, F, X, and "" to generate a valid constant and parser case for the empty value.

Validation

dotnet test tests/Kiota.Builder.Tests/Kiota.Builder.Tests.csproj --no-restore --nologo --filter 'FullyQualifiedName~CodeDOM.CodeEnumTests|FullyQualifiedName~Writers.Go.CodeEnumWriterTests|Name=ParsesEnumDescriptionsAsync' (14 passed)

Fixes #4329

[Copilot]

Pull request overview

This PR updates Kiota’s enum CodeDOM construction to preserve explicitly empty-string enum wire values (instead of dropping them), and adds regression tests to ensure the Go writer emits and parses the empty wire value correctly—addressing #4329.

Changes:

• Preserve empty-string enum values when building CodeEnumOption instances from OpenAPI schemas.
• Distinguish “explicitly set (possibly empty) serialization name” from “unset serialization name” in CodeEnumOption.
• Add tests covering empty-string enum option parsing/building and Go writer emission.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/Kiota.Builder/KiotaBuilder.cs	Stops filtering out empty enum values and assigns a stable option name for the empty wire value.
src/Kiota.Builder/CodeDOM/CodeEnumOption.cs	Tracks whether SerializationName was explicitly set (even if empty) to preserve empty wire names.
tests/Kiota.Builder.Tests/CodeDOM/CodeEnumTests.cs	Verifies explicit empty serialization name behavior in CodeEnumOption.
tests/Kiota.Builder.Tests/KiotaBuilderTests.cs	Ensures enum parsing retains an empty option and keeps its wire/serialization name empty.
tests/Kiota.Builder.Tests/Writers/Go/CodeEnumWriterTests.cs	Validates Go enum writer emits/handles the empty string wire value in String() and parser switch.