Collect all children processes dump in case of hang

[Evangelink]

From @MarcoRossignoli:

Current extension takes the dump only for the test host process. If hang of it is related to children hang looks complex understand the reason (we have only the tests that's hanging).
We should try to dump all children too.

[nohwnd]

vstest does this and the code is here: https://github.com/microsoft/vstest/blob/main/src/Microsoft.TestPlatform.Extensions.BlameDataCollector/WindowsHangDumper.cs#L38

https://github.com/microsoft/vstest/blob/main/src/Microsoft.TestPlatform.Extensions.BlameDataCollector/NetClientHangDumper.cs#L18

using minidump write dump on windows is preferable because it gives dumps also of processes that are not .net.