Add functional test for swift test --sanitize --filter failure

[Viditgupta-official]

Add functional test covering swift test --sanitize --filter failure

Motivation:

When running swift test on macOS with both --sanitize address and --filter enabled, test execution fails with the error:

Sanitizer load violates platform policy.

Running either flag independently works as expected, but the combination consistently fails. This behavior is currently undocumented and untested. Adding coverage ensures the issue is reproducible and prevents accidental regressions while the underlying cause is investigated.

Modifications:

Added a new functional test in TestDiscoveryTests

Used SwiftPM’s functional test harness to invoke swift test

Passed --sanitize address and --filter together

Asserted on the observed platform policy violation message

Guarded the test to macOS

Result:

The sanitizer + filter failure is now captured by SwiftPM’s test suite, making the behavior explicit and providing a stable foundation for future fixes or refactors.
Fixes #9546

[Viditgupta-official]

This PR intentionally only adds coverage for the sanitizer + filter behavior.
I plan to investigate the root cause of the sanitizer runtime loading failure in a follow-up change once this test is in place.

[Viditgupta-official]

Note: This test documents a known failure that appears to originate in the swiftpm-xctest-helper (an Xcode tool), not SwiftPM itself.

The test is intentionally added as coverage to prevent regressions and to make the behavior explicit while the underlying issue is tracked separately (via Apple Feedback).