feat(datepicker-actions): option to close on date selection or expose selectedChange on datepicker

#### Feature Description

Currently when a datepicker has a datepicker-actions component in it's content, it blocks the datepicker from closing on date selection. I'd like a way to have datepicker-actions in my datepicker component but still get the close on date selection behavior. There are 2 ways that I see of accomplishing this.

**Expose the `selectedChange` event that already exists on mat-calendar**
If the user had access to this they would easily be able to close the datepicker manually. Here's a usage example:
```html

Some static content for the user to read in the datepicker

```
It also makes sense to expose this now because before `datepicker-actions` the `datepicker` would close on selection, but now that it's held open, an app may need to do some logic on selection change and this would enable that.

**Add `closeOnSelection` input to `mat-datepicker-action`

Simply add a boolean input that allow datepicker-actions to be configured to close on selection. This one is more straightforward and probably easier for consumers to understand but not as versatile as the above solution.

#### Use Case

The most common use case would be when a consumer wants to put static content in the footer of the datepicker. Personally I am using `dateClass` to highlight dates I want to recommend for the user and want to put a key in the footer to describe what the different highlighted colors are supposed to indicate. I currently have to also add a `SELECT` and `CANCEL` button due to the way the datepicker behaves with actions, so my footer much bigger than it needs to be and the user has an extra click for each date they select.

#### Work

I've contributed before and have a pretty good idea how to implement either of the options presented above. So if the material team is interested please let me know which option would be best and I can start a PR.

首先，以 issue 中描述的两种 API 方案作为切入点，追踪 mat-datepicker、mat-calendar 的 selectedChange 事件和 mat-datepicker-actions 之间的交互。完成的标准是：使用清晰的面向消费者的 API 实现 maintainers 首选的行为，并且 datepicker 仍支持静态页脚内容，而无需额外的选择控件。

由索引模型根据 Issue 内容生成。