Hang when child process exits without writing to IPC pipe

After MSBuild starts a child/worker process, it [tries to handshake](https://github.com/Microsoft/msbuild/blob/d1bdd68a3f2b1eec2e9a17ec62ebe70c59e9019b/src/XMakeBuildEngine/BackEnd/Components/Communications/NodeProviderOutOfProcBase.cs#L412-L416) with the newly-created node by writing to an IPC pipe and waiting for the handshake response.

If process creation fails, an error is propagated upward and MSBuild doesn't hang. If, however, process creation succeeds but the child quickly terminates instead of waiting for the handshake, the indefinite blocking read on handshake response turns into a mysterious MSBuild hang.

We should either have a timeout for handshake success, or at the very least fail early in `WaitForConnectionFromProcess` if the `nodeProcessId` doesn't belong to a running process.

Start with the linked handshake code in src/XMakeBuildEngine/BackEnd/Components/Communications/NodeProviderOutOfProcBase.cs, especially WaitForConnectionFromProcess and the read after the IPC-pipe write. Trace what happens when the child exits before replying. Done means MSBuild fails early or times out instead of hanging indefinitely.

Written by the indexing model from the issue text.