feature(datepicker): Create a CDK version of the datepicker

It would be nice to create a cdk-datepicker that captures the interaction pattern of the various sub-components that make up the datepicker, but provides no concrete UI. It would be up to users (of which the Angular Material date-picker would be one) to build the actual UI and styling.

This is not something that we have any immediate plans to do, but I'm creating this issue to document it as something to consider in the future.

未指定任何文件、测试或入口点。首先检查现有的 Angular Material datepicker 和 Angular CDK 架构，以定义预期的无头交互模型；该 issue 未指定实现边界或完成标准。

由索引模型根据 Issue 内容生成。