Fix symbol anchor rendering by using Location instead of SymbolInformation in value property

[Copilot]

Symbol links in chat output (e.g., "activate function") failed to open with "Unable to resolve resource" errors showing malformed URIs like c:%5CUsers%5C....

Root Cause

ChatResponseAnchorPart was constructed with SymbolInformation cast to any where VS Code expects Uri | Location, causing the chat UI to extract properties incorrectly.

// Before: Passing SymbolInformation where Uri | Location expected
const chatPart = new ChatResponseAnchorPart(part.symbolInformation as any);

Changes

File: src/extension/linkify/common/responseStreamWithLinkification.ts

• Pass symbolInformation.location to constructor for the value property (backward compatible)
• Set value2 property to full SymbolInformation for proper symbol rendering (proposed API)

// After: Proper type handling with proposed API support
const chatPart = new ChatResponseAnchorPart(part.symbolInformation.location);
(chatPart as any).value2 = part.symbolInformation;

This aligns with vscode.proposed.chatParticipantAdditions.d.ts where value2 supports Uri | Location | SymbolInformation.

Testing

Added responseStreamWithLinkification.spec.ts with tests covering:

• Symbol anchors set both value (Location) and value2 (SymbolInformation)
• Regular location anchors continue working without value2

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Unable to open file resource from chat output</issue_title>
<issue_description>Found while testing microsoft/vscode#280380, though mostly unrelated to the TPI

• Use Copilot Chat to support me while I work on the TPI
• It provides a link so that I can specifically look at the activate function in my code
• ❓ Link doesn't resolve

Attaching logs from Show Logs above: Dec 2 logs 1.txt</issue_description>

Comments on the Issue (you are @copilot in this section)

@bamurtaugh The other links below in the chat output do open properly:

</comment_new>

• Fixes Unable to open file resource from chat output vscode#280686

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.