Add SharedVariables to pipeline simulation

[jordimontana82]

While FakeXrmEasy supports passing in SharedVariables in ExecutePlugin** methods via your own XrmFakedPluginContext instances, the current implementation of pipeline simulation ignore SharedVariables that could be passed between plugins.

Some background info:

"Official" at SharedVariables section in https://learn.microsoft.com/en-gb/power-apps/developer/data-platform/understand-the-data-context.

Other Blogs / Experiences
https://www.itaintboring.com/dynamics-crm/shared-variables-in-dataverse-plugins-surprise-surprise/
https://carldesouza.com/tag-shared-variable-custom-values-web-api-plugins/
https://xrmdynamicscrm.wordpress.com/2020/06/02/dynamics-365-shared-variables-pass-data-between-plugins/