Add new utilities for grid-auto-columns and grid-auto-rows

[adamwathan]

This PR adds a new set of utilities for the grid-auto-columns and grid-auto-rows properties:

Class	CSS
auto-cols-auto	grid-auto-columns: auto
auto-cols-max	grid-auto-columns: max-content
auto-cols-min	grid-auto-columns: min-content
auto-cols-fr	grid-auto-columns: minmax(0, 1fr)
auto-rows-auto	grid-auto-rows: auto
auto-rows-max	grid-auto-rows: max-content
auto-rows-min	grid-auto-rows: min-content
auto-rows-fr	grid-auto-rows: minmax(0, 1fr)

These are configurable under the gridAutoColumns and gridAutoRows keys respectively. Only responsive variants are generated by default.