This PR adds a block-enabled theme with templates for WooCommerce
which is intended to be used when testing the more complex scenarios
such as template fallbacks.
Additionally, since theme-dependent logic seems to be becoming more
and more useful (see woocommerce/woocommerce-blocks#5913), this PR also adds a utility function used to
explicitly declare theme dependencies of a test (`useTheme`).
Said function will activate the theme before running a given suite and then
reactivate the previous theme, as to make sure to not have any side-effects
(such as the ones described in woocommerce/woocommerce-blocks#5913 above).
Closeswoocommerce/woocommerce-blocks#5660
Lucio Giannotta