Make issue/PR references clickable in @githubpr chat output

[Copilot]

Issue and PR numbers in @githubpr chat responses appear as plain text (e.g., "This PR addresses issue #7280"), preventing users from quickly navigating to referenced issues.

Changes

• Added convertIssuePRReferencesToLinks() in src/common/uri.ts

  • Converts patterns like #123, issue 123, issue #123, PR 123, PR #123 to markdown links
  • Uses word boundaries to avoid false matches (e.g., won't match not#123)
  • Case-insensitive matching for keywords

• Integrated link conversion in chat output processing

  • chatSessionContentBuilder.ts: Applied to historical chat content when loading sessions
  • copilotRemoteAgent.ts: Applied to streaming responses during active sessions

• Added comprehensive unit tests covering various reference patterns and edge cases

Example

Input text:

This PR addresses issue #7280. See also PR 100 and issue 200.

Output markdown:

This PR addresses issue [#7280](https://github.com/owner/repo/issues/7280). 
See also [PR 100](https://github.com/owner/repo/issues/100) and 
[issue 200](https://github.com/owner/repo/issues/200).

[!WARNING]

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• update.code.visualstudio.com
  • Triggering command: /opt/hostedtoolcache/node/20.19.6/x64/bin/node node ./out/src/test/runTests.js --grep convertIssuePRReferencesToLinks (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Issue link should be clickable in @githubpr chat output</issue_title> <issue_description>

I've been chatting with @githubpr about my PR and what it knows.

It'd be great for the issue number 7280 at the end to be clickable:

</issue_description>

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

@alexr00 We should scan the output for things that look like an issue or PR number and convert them to issue and PR urls using the functions in uri.ts.

• Fixes microsoft/vscode-pull-request-github#7333

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