Guidelines: reuse UserControls - psjw12/gitextensions GitHub Wiki
Here we describe ready to reuse user controls.
FolderBrowserButton
For folder browsing button there already is a user control: UserControls.FolderBrowserButton.
Via designer you can set the property PathShowingControl (e. g. a textbox or combobox). SelectedPath from FolderBrowserDialog will be set from the PathShowingControl's Text property and the vice versa automatically.