Fix preview API version detection for const-based codegen pattern

[Copilot]

autorest.go#1944 moved API version literals from inline usage to per-client consts, breaking containsPreviewAPIVersion in the generator.

Before (inline literal — old codegen):

reqQP.Set("api-version", "2023-01-01-preview")

After (const declaration — new codegen):

const defaultFooClientVersion string = "2023-01-01-preview"
// ...
reqQP.Set("api-version", defaultFooClientVersion)

The detector only matched the inline pattern via "api-version" string splitting, so it stopped finding preview versions in newly generated code.

Changes

• Added apiVersionConstRegex to match const default<Name>Version string = "..." declarations
• containsPreviewAPIVersion now checks both the inline and const patterns
• Added test cases covering const-based preview and stable version detection

[Chenjie Shi (tadelesh)]

Could you add the changelog and bump version?

[Copilot]

Pull request overview

This PR updates the generator’s preview API version detection logic to recognize a const-based API version pattern (in addition to inline "api-version" usage), and adds unit tests for the new detection case.

Changes:

• Add apiVersionConstRegex and extend containsPreviewAPIVersion() to detect preview API versions declared via a default*Version const.
• Add unit tests covering preview/stable const-based API version declarations.
• Apply gofmt alignment changes in the regex var block.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
eng/tools/generator/version/version_tool.go	Adds a new regex and detection branch for const-based preview API version detection.
eng/tools/generator/version/version_tool_test.go	Adds tests to validate the new const-based detection behavior.

[Jiaqi Zhang (JiaqiZhang-Dev)]

Could you add the changelog and bump version?

Copilot pls help add the changelog and bump version for generator

[Copilot]

Could you add the changelog and bump version?

Copilot pls help add the changelog and bump version for generator

Done — bumped version to v0.4.11 in version.go and added the changelog entry in commit 2250f9d.

[Chenjie Shi (tadelesh)]

How could current logic handle multiple services case?

[Copilot]

How could current logic handle multiple services case?

containsPreviewAPIVersion iterates all .go files in the package directory and returns true if any file contains a preview API version (either inline or const pattern). So for multiple services/clients, the package is considered preview if any client has a preview version. This is the pre-existing behavior — this PR only adds the const-based detection pattern.