Problem to solve

Currently VDatePicker is missing a readonly property. Adding one would allow for the DatePicker to still be navigable, while not allowing for inputs to be changed. The only option currently available is the disabled property, but that prevents changing the year or months.

Proposed solution

Add a readonly property, similar to VTimePicker. This change should allow for calendar navigation, while not allowing the value(s) to change.

See: https://play.vuetifyjs.com/#eNrdk81OwzAQhF/F8qWXOH9VJahCERJ3JK5tD9t4aQyOY9lOEEK8O3ab1ongjsTN8+144x1lt5/Umjp70DodeqRrWjlstQSHm50ipBoYaH06nkTdKQdCoRmRh9aZTh03zwicPCn5cV9lI7paBsZ9Q6ZF/YbmQglZtx1HyQaQPd7t6HZR5uWKFQUrbxcJuaplHlXJisV+R2OPtpdOaBnuG1BHnNbACGDGv6vzz/IGZ/pZfW2b7p0Bf4UalWOtn62xv/guLSJpBEfWeDwdByUO4ESnfIt8ev/kdsJJjKyWYMO3NLBojYlls8giPxiS/Yj+UVg4SOT/Lng+DvbXwQc6//MDOS9GlU0WxktbG6Edsej6UA6GM/KCfiV0ma7SsqThUOTpDU1eQFpMZlt4Zvtvb/oNOw==