Allow specifying the msbuild binlog path when invoking static graph restore to avoid modifying the environment

[ViktorHofer]

Details about Problem

NuGet product used (NuGet.exe | Visual Studio | MSBuild.exe | dotnet.exe): dotnet.exe

Product version: 6.0.100-preview.3.21202.5

Worked before? If so, with which NuGet version:

Repro steps and/or sample project

When using static graph restore, the environment variable RESTORE_TASK_BINLOG_PARAMETERS needs to be set to generate a binlog for the out-of-process evaluation of the projects. If you are already inside an msbuild instance, it's not possible to modify the existing environment variables without a custom task (either compiled or inline).

To avoid modifying the existing environment, RestoreTaskEx task could accept a property to specify the path to the restore binlog which is then passed in as an environment variable to the restore task console.

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