Preserve AggregateError nested errors in reporter output

[charliesheh]

Summary
Preserve AggregateError.errors[] entries when filtering and serializing stack traces for reporter output.
Previously, filterStackTrace() recursively preserved error.cause, but omitted nested errors contained in AggregateError.errors[].

Changes

• Added recursive serialization support for AggregateError.errors[]
• Preserved nested aggregate sub-errors in reporter output
• Added regression coverage in reporter-base.spec.ts

Testing

• npm run build
• npm run ttest -- tests/playwright-test/reporter-base.spec.ts

[charliesheh]

@microsoft-github-policy-service agree