Split variable $table-cell-padding into separate variables

The variable $table-cell-padding is used both for table cells and for the table caption. The padding shorthand property, used in cells, allows us to declare multiple values in this variable. But in such case it leads to the syntax error for the table caption where the individual padding properties (padding-top & padding-bottom) are defined. To solve this issue, we can create separate variables for both elements or at least for two directions ($table-cell-padding-x, $table-cell-padding-y).