Print paths to response files in message

It would be really nice if this message were parameterized instead of always saying `MSBuild.rsp`. It should print the (possibly multiple) response files considered.

```
Some command line switches were read from the auto-response file "MSBuild.rsp". To disable this file, use the "/noautoresponse" switch.
```

Start by searching the MSBuild source for the shown message, then trace how response files are collected. Check nearby command-line or response-file tests; done means the diagnostic lists every considered response-file path and still explains how to disable automatic response-file loading.

Written by the indexing model from the issue text.