Explore how to support custom breakpoints

[weinand]

There are a few feature requests around customising breakpoints and their interaction, e.g.:

• Support an extension point for customizing gutter interaction. #38568: Support an extension point for customizing gutter interaction
• Visualize breakpoint types in breakpoints viewlet #42266: Visualize breakpoint types in breakpoints viewlet
• Feature Request: Custom Breakpoints For Extensions #10447: Custom Breakpoints For Extensions
• Add support for LogPoints in Node vscode-node-debug2#163: Add support for LogPoints
• Enable debug adaptors to enable/disable certain breakpoint types vscode-debugadapter-node#155: Enable debug adaptors to enable/disable certain breakpoint types

Opening up all breakpoint functionality for customisation does not seem to be a sustainable approach because it would surface many VS Code implementation details as API.

As an alternative approach we will explore in February how to contribute a new breakpoint type from an extension and how to support it like the existing built-in types.

[weinand]

In the February milestone we have explored custom breakpoints based on the example "LogPoints".
The discussion and plan can be found here microsoft/vscode-node-debug2#163

So the first February exploration has been finished but I will keep the item "On Deck" as we continue exploring this after we have implemented LogPoints in March 2018.

[weinand]

since LogPoints have been implemented and since rich breakpoint API already exists, we do not intend to work on this.