vcvars with powershell (#3541)

Author: juansblanco

reference/tools/microsoft/vcvars.rst

@@ -52,6 +52,7 @@ conf
 - ``tools.microsoft.msbuild:installation_path`` indicates the path to Visual Studio installation folder.
   For instance: ``C:\Program Files (x86)\Microsoft Visual Studio\2019\Community``, ``C:\Program Files (x86)\Microsoft Visual Studio 14.0``, etc.
 - ``tools.microsoft:winsdk_version`` defines the specific winsdk version in the vcvars command line.
+- ``tools.env.virtualenv:powershell`` generates an additional ``conanvcvars.ps1`` so it can be run from the Powershell console.
 
 Reference
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