Fix possible ToolTask hang

[MichalPavlik]

Fixes #2981
and probably #10286

Context

ToolTask can hang when child process spawns a grandchild process that doesn't exit.

Changes Made

Using different overload of WaitForExit to avoid situation when grandchild process is keeping the MSBuild waiting.
See dotnet/runtime#51277 and #2981 (comment)

Testing

Manual testing with custom ToolTask implementation. This tasks starts process that starts another process with longer lifetime.

Notes

[rainersigwald]

Remember how you mentioned this offline and said "I bet Rainer will ask for {some wise thing to ask}"?

. . . let's assume I ask for that :-P

(Was it a wait-for-flush situation? I don't know if there's a great way to do that. Maybe just putting this behind a changewave would be sufficient?)

[Kuinox]

I remember that when I analyzed the problem, the issue of WaitForExit(int) is that it doesn't wait for the pipes to empty.

I'm not sure, but I think it can lead to the end of the output to be truncated.

[akoeplinger]

I'm not sure, but I think it can lead to the end of the output to be truncated.

I think I'm running into this issue after this PR: #10378

[Kuinox]

There could be a work around using some reflection hack, but without that there is no way to wait for exit cleanly on windows.

Ideally the underlying bug should be fixed: dotnet/runtime#51277