There are a few ways. Do you really need a library project? Using the library in your project code and clicking the vmicro>show/hide hidden files option will give you access to the lib code in the project but without being fixed to a specific set of library files and version.

If you really want a project with the library then ...

If the library is in the standard arduino lib locations then use the advanced feature on the add library menu to enable "create shared project" option. Then click to add the library as normal. Switch the option off again after you use it. Normally you don't want

or Manually add a new "Visual Studio Shared C++" project (.vcxitems) to the library root using the standard Visual Studio File>New>project feature. Ensure the name is the same name as the library folder such as SPI. When you create and add a shared c++ project file to the solution you can use the "show all files" icon to right click include or exclude the sources of the library. You then need to right click the References node of your arduino project(s) and then click "Add Reference". On the add reference window there is a tab on the left side called "Shared Projects". That allows you to select which of the shared projects in the current solution are to be referenced by the arduino code. 

Make sense?

This doc page is due to be updated but shows explains some of this.

https://www.visualmicro.com/post/2017/01/16/Arduino-Cross-Platform-Library-Devel...