paginator 概览
<mat-paginator> 可以为分页信息提供导航功能，通常和表格一起用。
<mat-paginator> provides navigation for paged information, typically used with a table.
每个分页器实例都需要：
Each paginator instance requires:
每页的条目数（默认为 50）
The number of items per page (default set to 50)
要分页的总条目数
The total number of items being paged
当前页的索引默认为 0，不过可以通过 pageIndex 进行显式设置。
The current page index defaults to 0, but can be explicitly set via pageIndex.
当用户与分页器交互时，将会触发一个 PageEvent，你可以根据它更新相关的数据视图。
When the user interacts with the paginator, a PageEvent will be fired that can be used to update
any associated data view.
分页器会显示一个页大小的下拉框，让用户可以选择页大小。该下拉框的选项可以通过 pageSizeOptions 进行设置。
The paginator displays a dropdown of page sizes for the user to choose from. The options for this
dropdown can be set via pageSizeOptions
即使没有在 pageSizeOptions 中指定页大小，它也总会显示在下拉框中。
The current pageSize will always appear in the dropdown, even if it is not included in pageSizeOptions.
分页器的各种标签可以通过指定你自己的 MatPaginatorIntl 实例进行定制。
这将允许你修改：
The labels for the paginator can be customized by providing your own instance of MatPaginatorIntl.
This will allow you to change the following:
每页大小的标签。
The label for the length of each page.
要显示给用户的范围文本。
The range text displayed to the user.
各个导航按钮上的提示信息。
The tooltip messages on the navigation buttons.
The paginator uses role="group" to semantically group its child controls. You must add an
aria-label or aria-labelledby attribute to <mat-paginator> with a label that describes
the content controlled by the pagination control.
You can set the aria-label attributes for the button and select controls within the paginator in
MatPaginatorIntl.