Function does not handle paths with whitespace

This function cannot handle paths with whitespace. It will truncate at the first location with whitespace. The doc says nothing about this.

Attempting to quote such a path throws an ArgumentException because the quotes are illegal characters.

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#### Document Details

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* ID: f5f481a9-6cdc-49c0-098b-08e639f1e161
* Version Independent ID: 43b2e376-a7d2-29fa-4012-3934bf931fc4
* Content: [Path.GetDirectoryName Method (System.IO)](https://docs.microsoft.com/en-us/dotnet/api/system.io.path.getdirectoryname?view=netcore-2.1#System_IO_Path_GetDirectoryName_System_String_)
* Content Source: [xml/System.IO/Path.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.IO/Path.xml)
* Product: **dotnet-api**
* GitHub Login: @dotnet-bot
* Microsoft Alias: **dotnetcontent**