Fix #2793: Use proper FQN in VS Test Explorer to avoid hierarchy split

[Shrinidhi203]

Summary

• Fix incorrect VS Test Explorer hierarchy when job display name contains . (e.g., ".NET 8.0.6")
• Detect Visual Studio environment via VSAPPIDNAME environment variable
• Use benchmark method FQN instead of displayName for test case in VS, preventing dots in job names from being
  misinterpreted as namespace separators
• Preserve existing Rider/R# workaround (Rider and R# do not distinguish parametrized TestAdapter cases #2494) for non-VS environments

Test plan

• Added unit tests for BenchmarkCaseExtensions.ToVsTestCase:
  • ToVsTestCase_WithoutVSAPPIDNAME_UsesDisplayNameAsFQN
  • ToVsTestCase_WithVSAPPIDNAME_UsesMethodFQNToAvoidHierarchySplit
  • ToVsTestCase_WithVSAPPIDNAME_FQNDoesNotContainDotFromJobName