Support Activity Events and Links trace out of proc output

[tarekgh]

Fixes #102924

• System.Diagnostics.Activity out of proc monitoring can't access Activity Events or Links #102924

This change supports formatting the Events and Links embedded in the Activity object to allow getting such formatted data when the activity data gets serialized out of proc. The Events and Links will show up like the following example in the ETW serialized data:

Events->"[(TestEvent1,​2025-03-27T23:34:10.6225721+00:00,​[E11:​EV1,​E12:​EV2]),​(TestEvent2,​2025-03-27T23:34:11.6276895+00:00,​[E21:​EV21,​E22:​EV22])]"
Links->"[(19b6e8ea216cb2ba36dd5d957e126d9f,​98f7abcb3418f217,​Recorded,​null,​false,​[alk1:​alv1,​alk2:​alv2]),​(2d409549aadfdbdf5d1892584a5f2ab2,​4f3526086a350f50,​None,​null,​false)]"

Note: the Events and Links will have the zero width space \u200B embedded after , and :.

[Copilot]

Pull Request Overview

This PR supports formatted output of Activity Events and Links for out-of-proc serialization. It adds new tests for verifying the formatting, updates the DiagLinkedList string conversion logic for ActivityLink and ActivityEvent types, adjusts the instantiation of empty collections in Activity.cs, and fixes a comment typo in TimeZoneInfo.cs.

Reviewed Changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/libraries/System.Diagnostics.DiagnosticSource/tests/ActivityTests.cs	Introduces new tests to validate the ToString output for Activity Links and Events.
src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/DiagLinkedList.cs	Adds helper functions for converting ActivityLink and ActivityEvent objects to a formatted string.
src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/ActivitySource.cs	Removes an unnecessary check for listeners.
src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Activity.cs	Replaces array initializations with DiagLinkedList for empty collections.
src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.cs	Corrects a typo in a comment to match the intended variable name.

Files not reviewed (1)

• src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj: Language not supported

Comments suppressed due to low confidence (1)

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.cs:980

• The comment now correctly spells 'daylightDisplayName'. Ensure that similar typos are corrected consistently in documentation if applicable.

                          <_standardDisplayName>;<_daylightDisplayName>;

[tarekgh]

@noahfalk @CodeBlanch @rajkumar-rangaraj could you please have a look at the change? Thanks!

[noahfalk]

This is fine by me as long as our OTel.NET crew is happy with the serialized data format.

[tarekgh]

@rajkumar-rangaraj @noahfalk @CodeBlanch is there anything that needs to be addressed, or can you approve it?

[rajkumar-rangaraj]

LGTM