Add VSCode extension for BSP server log streaming

[joshua-arnold]

Summary

Adds a companion VSCode extension that streams logs from the SourceKit Bazel BSP server directly into a VSCode output channel, making it easier to monitor and debug BSP server activity without leaving the editor.

Motivation

At the moment, this extension only outputs important logs (errors) to VSCode tab. This will make it easy for people to identify errors instead of needing to setup a log stream and parse the large output.

Furthermore, we will be able to log other important warnings & information when needed.

Moving forward, hopefully we can start to support the remaining functionality in this extension:

• Cursor / VSCode): Automatic generation of build, launch, and debug tasks
• (Cursor / VSCode): Test explorer & ability to run tests from within the IDE by clicking the tests individually, similarly to Xcode
• Automatic index and build graph updates when adding / deleting files and targets (in other words, allowing the user to make heavy changes to the project without needing to restart the IDE)

Changes

• New VSCode extension (vscode-extension/)

  • Streams BSP server logs using macOS log stream command
  • Filters logs by subsystem (com.spotify.sourcekit-bazel-bsp) and category (extension)
  • Parses and formats log output for clean display in the "SourceKit Bazel BSP" output channel
  • Automatically starts on extension activation and cleans up on deactivation

• New extension logger (Sources/SourceKitBazelBSP/SharedUtils/Logger.swift)

  • Added extensionLogger for user-facing messages intended to be shown in the VSCode extension
  • Refactored subsystem constant for reuse

• CI updates (.github/workflows/ci.yaml)

  • Added step to build and compile the VSCode extension

Test plan

Tested the extension in the example project:

[rockbruno]

Thanks @joshua-arnold! I'll give this a deeper look over the following days!

[josh-arnold-1]

Thanks! No problem also if we want to go in another direction, just wanted to propose to get the ball rolling as I feel like the extension would be useful for eventually auto generating launch tasks etc, test running integration, + custom logic for detecting when new build files are added / modified in the work space etc.

[joshua-arnold]

@rockbruno updated! The extension should be super bare-bones now, ready to be built on top of. I also added some basic CI steps that ensure it will compile without warnings.