[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)

Start by searching the Angular CDK table implementation and tests for `cdk-header-row` and `cdk-row` template handling. Verify the behavior for a table with no header, a table with no data-row template, and a header-only table; done means omitted templates are not inserted while supported rows still render.

Written by the indexing model from the issue text.