Move DatePicker to a polyglot module

[beaucollins]

The DatePicker iOS/Android views are defined in Valdi Open Source. The Component module code is in this repository and is a fork that is drifting.

Create a Polyglot module that contains both the Valdi Component code and native backing views for the <custom-view>.

For reference:

• iOS Native view in Valdi
• Android Native view in Valdi
• DatePicker Component Code

[clholgat]

Done.