Support running tests locally in a helix environment on Linux

[MichaelSimons]

1. Add execute permission to sdk-build-env.sh and RunTestsOnHelix.sh
2. Remove the PayloadDirectory metadata from the HelixCorrelationPayload. This is not supported by Helix and is something sdk added. The CreateLocalHelixTestLayout task had a hard dependency on the PayloadDirectory yet is wasn't specified for every HelixCorrelationPayload. The CreateLocalHelixTestLayout was updated to depend on the include metadata instead.

[Copilot]

Pull request overview

This pull request enables running SDK tests locally in a Helix environment by simplifying the payload handling mechanism and ensuring proper script permissions.

Changes:

• Removed the non-standard PayloadDirectory metadata from HelixCorrelationPayload items
• Updated CreateLocalHelixTestLayout task to use ItemSpec directly instead of PayloadDirectory metadata
• Added execute permissions to generated sdk-build-env.sh script

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 1 comment.

File	Description
test/UnitTests.proj	Removed PayloadDirectory metadata from all HelixCorrelationPayload items, simplifying the configuration
test/HelixTasks/CreateLocalHelixTestLayout.cs	Refactored to use ItemSpec directly, added file/directory handling logic, and improved cleanup behavior
eng/restore-toolset.sh	Added chmod +x to ensure the generated build environment script is executable
build/RunTestsOnHelix.sh	New script for running tests on Helix in POSIX environments