Host: log exception if a service factory fails

[mus65]

Currently, the host doesn't log any exception if a IHostedService or IStartupValidator service factory fails. If you use RunAsync you also have no way to log it yourself since the host has already been disposed after it returns (see also #72225).

This catches any exceptions thrown by the GetService calls and logs and re-throws the exception, similiarly on how it is already done for exceptions in StartAsyncetc. .

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Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

[steveharter]

I would recommend either removing this return, or making it consistent with the rest of the code here.

There's also [DoesNotReturn] that can be applies to LogAndRethrow() but that would be just for readability in this case I believe.

[mus65]

The return; is necessary here to avoid a null reference warning for _hostedServices below. [DoesNotReturn] is not possible because LogAndRethrow() does not actually throw if exceptions is empty.

[steveharter]

cc @halter73 for any feedback. Thanks