Add new command for LSP/Webview integration

[noklam]

Context

Fix ##56

This allow integration Click on Webview -> Navigation feature.

Development Notes

• Develop a separate command that to be called by the Webview (frontend)
• The command should be called via the Webview API https://code.visualstudio.com/api/extension-guides/webview#scripts-and-message-passing

Additional Notes

Base on some investigation, it seems that we need to manually handle the response from LSP instead of automatically trigger navigation. I am unsure where to find internal wiring of VSCode (where you do Cmd + click to trigger navigation, and the response is used to trigger action).

Trigger flow

1. Request send to LSP (from command in this PR, expected to be a click on Webview at the end)
2. LSP respond with location
3. Extension react to the response and use showTextDocument based on the command.

A new command is created mainly for testing purpose, we don't need the command for release (or we can keep it as a debug mode feature)