Add msbuild instrumentation task debugging mode (#631)

Add msbuild instrumentation task debugging mode

Documentation/Troubleshooting.md

@@ -223,3 +223,16 @@ We can collect logs from trackers through an enviroment variable
 ```
 When enabled, tracking event will be collected in log file near to module location.  
 File name will be something like `moduleName.dll_tracker.txt`
+
+## Enable msbuild task instrumentation debugging
+
+You can live attach and debug msbuild tasks with `COVERLET_MSBUILD_INSTRUMENTATIONTASK_DEBUG` env variable
+```
+ set COVERLET_MSBUILD_INSTRUMENTATIONTASK_DEBUG=1
+```
+You'll get this message during test run
+```
+dotnet test  -p:Include="[test_coverage.]"   -p:Exclude="[*.Test.*]*"   -p:CollectCoverage=true   -p:CoverletOutputFormat=cobertura   -p:CoverletOutput=coverage.cobertura.xml
+Coverlet msbuild instrumentation task debugging is enabled. Please attach debugger to process to continue
+Process Id: 29228 Name: dotnet
+```

src/coverlet.msbuild.tasks/InstrumentationTask.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics;
 using System.IO;
 
 using Coverlet.Core;
@@ -97,8 +98,27 @@ namespace Coverlet.MSbuild.Tasks
             _logger = new MSBuildLogger(Log);
         }
 
+        private void WaitForDebuggerIfEnabled()
+        {
+            if (int.TryParse(Environment.GetEnvironmentVariable("COVERLET_MSBUILD_INSTRUMENTATIONTASK_DEBUG"), out int result) && result == 1)
+            {
+                Console.WriteLine("Coverlet msbuild instrumentation task debugging is enabled. Please attach debugger to process to continue");
+                Process currentProcess = Process.GetCurrentProcess();
+                Console.WriteLine($"Process Id: {currentProcess.Id} Name: {currentProcess.ProcessName}");
+
+                while (!Debugger.IsAttached)
+                {
+                    System.Threading.Tasks.Task.Delay(1000).Wait();
+                }
+
+                Debugger.Break();
+            }
+        }
+
         public override bool Execute()
         {
+            WaitForDebuggerIfEnabled();
+
             try
             {
                 var includeFilters = _include?.Split(',');