Improve debug console output when building the debuggee in DAP

[gfszr]

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Delve version: 1.9.1

Right now, when using a simple launch configuration such as:

{
        "name": "debug main",
        "type": "go",
        "request": "launch",
        "mode": "debug",
        "program": "${workspaceFolder}/main.go",
}

The delve debug adapter first builds the program in the background and then launches it, and in case the build fails it sends an OutputEvent back indicating the error. On large projects, building might take some time, so better clarification can be much helpful when just waiting for the launch request to finish. I suggest output events indicating that a build is happening, perhaps with the build command line, just as output events are sent if there's an error.

[gfszr]

@aarzilli I might be able to help with that one, if you have any guidelines before working on it 👍

[aarzilli]

It happens inside onLaunchRequest. GoBuildCombinedOutput and GoTestBuildCombinedOutput themselves can not be changed because they are used elsewhere.