Fix MSBuild target display stuck on InstallTspClient during code generation

[Copilot]

When running dotnet build /t:GenerateCode, MSBuild's terminal logger displays "InstallTspClient" throughout the entire generation process instead of transitioning to "GenerateCode" after installation completes.

Changes

eng/CodeGeneration.targets:

• Changed GenerateCode target to use DependsOnTargets="InstallTspClient" instead of CallTarget
• Moved SkipTspClientInstall condition to InstallTspClient target definition

Before:

<Target Name="InstallTspClient" Condition="'$(TypeSpecInput)' != ''">
  <Exec Command="npm ci --prefix $(_TspClientDir)" />
</Target>

<Target Name="GenerateCode" Condition="'$(TypeSpecInput)' != ''">
  <CallTarget Condition="'$(SkipTspClientInstall)' != 'true'" Targets="InstallTspClient" />
  <Exec Condition="..." Command="..." />
</Target>

After:

<Target Name="InstallTspClient" Condition="'$(TypeSpecInput)' != '' AND '$(SkipTspClientInstall)' != 'true'">
  <Exec Command="npm ci --prefix $(_TspClientDir)" />
</Target>

<Target Name="GenerateCode" Condition="'$(TypeSpecInput)' != ''" DependsOnTargets="InstallTspClient">
  <Exec Condition="..." Command="..." />
</Target>

Using DependsOnTargets allows MSBuild to properly track target transitions instead of maintaining the calling target's context through CallTarget.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>InstallTspClient target displayed the whole time while generating</issue_title>
<issue_description>For some reason the InstallTspClient target is shown the whole time, instead of just for the first step in the generation process. It should show GenerateCode afterwards but it doesn't do this.

C:\Users\jolov\repos\azure-sdk-for-net\sdk\documentintelligence\Azure.AI.DocumentIntelligence\src [main ≡ +0 ~2 -0 !]> dotnet build /t:GenerateCode -v d
Restore complete (0.9s)
    Determining projects to restore...
    All projects are up-to-date for restore.
  Azure.AI.DocumentIntelligence                                                                InstallTspClient (44.6s)
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes InstallTspClient target displayed the whole time while generating #53504

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[Copilot]

Pull Request Overview

This PR refactors the MSBuild target dependencies for TypeSpec code generation by simplifying how InstallTspClient is invoked. Instead of conditionally calling the target from within GenerateCode, it establishes a proper dependency relationship between the targets.

Key Changes:

• Added SkipTspClientInstall condition to the InstallTspClient target definition
• Changed GenerateCode to depend on InstallTspClient via DependsOnTargets attribute
• Removed the conditional CallTarget invocation from within GenerateCode

[weshaggard]

/check-enforcer evaluate