Implement event_breakpoint in nvim-dap

[mxsdev]

Unlike many other dap based adapters, vscode-js-debug always communicates breakpoints as initially unverified (rejected), until this is changed layer with the breakpoint event. This is in order to support multiple child sessions, where the rejection status of a breakpoint may not be known until much after the initial setBreakpoints request.

This plugin currently "solves" this problem by hijacking the nvim-dap event loop and setting all breakpoints as initially verified, and then rechecking the status once a continued event is received. This solution is hacky and probably has some edge cases (particularly when there are multiple child sessions of interest).

This is essentially an issue with nvim-dap, so a parallel PR over there will be made eventually. I am cross-posting this here for the sake of tracking the issue.

[mfussenegger]

Does mfussenegger/nvim-dap#620 resolve this or is there more required to get this working?