New Command Line Parameter @file

[christophwille]

Similar to @file in https://learn.microsoft.com/en-us/visualstudio/msbuild/msbuild-command-line-reference?view=vs-2022 with equally similar format in https://learn.microsoft.com/en-us/visualstudio/msbuild/msbuild-response-files?view=vs-2022

In-house use case: the VS Addins could create a tempfile.rsp when passing super-long parameter lists instead of the current native interop way. Benefit: anyone can create such files.