Add Quantity Input to the WooCommerce Shop Page (simple products only) Without A Template Override

gistfile1.php

add_action( 'woocommerce_before_shop_loop_item', 'beardedguy_add_quantity_input' );

function beardedguy_add_quantity_input() {
	global $product;
	$product_type = ( version_compare( WC_VERSION, '3.0', '<' ) ) ? $product->product_type : $product->get_type();
	if ( 'simple' == $product_type ) {
		remove_action( 'woocommerce_after_shop_loop_item', 'woocommerce_template_loop_add_to_cart', 10 );
		add_action( 'woocommerce_after_shop_loop_item', 'woocommerce_template_single_add_to_cart', 10 );
	} else {
		remove_action( 'woocommerce_after_shop_loop_item', 'woocommerce_template_single_add_to_cart', 10 );
		add_action( 'woocommerce_after_shop_loop_item', 'woocommerce_template_loop_add_to_cart', 10 );
	}
}