[Table] Remove requirement for a header or data row template

It's valid that tables may not want any header, or a table could *only* be a header. Support this use case by letting users avoid defining a `cdk-header-row` or `cdk-row` which means that they should not be inserted.

Motivation: A table footer row could be a single row composed of a single row without a header. If placed after a preceding table, it acts as a sticky footer. Works well for cases where the header should not affect the rows, e.g. a totals row

Note that this doesn't help in cases where a scrollbar appears on one container but not the other. This will cause misalignment on browsers that push content left to show a scrollbar rather than overlay it (e.g. safari)

首先搜索 Angular CDK 的表格实现和测试，查找 `cdk-header-row` 和 `cdk-row` 模板的处理方式。验证没有表头的表格、没有数据行模板的表格以及仅有表头的表格的行为；当省略的模板不会被插入，而受支持的行仍会渲染时，即表示完成。

由索引模型根据 Issue 内容生成。