[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)

[zdzarsky]

I want to have a key-value table with no header.

[Lakston]

I personally went the display route like this

<mat-header-row 
    *cdkHeaderRowDef="['col1', 'col2']"
    style="display: none;">
</mat-header-row>

and it works fine on all browsers, I use the paginator so I didn’t encounter any problems regarding the scroll bar since well, I don’t have one.