Can MSB4166 error include the PID of the crashed node?

Thought of this while looking at [AB#1247204](https://devdiv.visualstudio.com/0bdbc590-a062-4c3f-b0f6-9383f67865ee/_workitems/edit/1247204).

When a child node crashes, we get a message like

```
“Child node “7” exited prematurely. Shutting down. Diagnostic information may be found in files in “C:\Users\someone\AppData\Local\Temp” and will be named MSBuild_*.failure.txt.”.
```

The naming pattern for those files includes the PID but not the logical node number. It'd be nice if the PID was included in the message so you could jump right to the file in question.

Search the MSBuild source for MSB4166 and the child-node crash message. Trace how the diagnostic filename is formed, then update the relevant error message so it includes the crashed node's PID; confirm the resulting message points to the matching MSBuild_*.failure.txt file.

Written by the indexing model from the issue text.