"Qty Uses Decimals" doesn't work for simple product

[smoskaluk]

Preconditions

1. Magento MSI
2. Simple product created

Steps to reproduce

1. In "Advanced Inventory" enable "Qty Use Decimals" for your simple product
2. Go to home page and open simple product page
3. Try to add to cart simple product with qty 1.23

Expected result

1. Product should be added to the cart

Actual result

1. Error message: The requested qty is not a valid increment
   

[OlgaBurtyka]

I see some other error

[maghamed]

We have next code

        /**
         * Check quantity type
         */
        $result->setItemIsQtyDecimal($stockItem->getIsQtyDecimal());
        if (!$stockItem->getIsQtyDecimal()) {
            $result->setHasQtyOptionUpdate(true);
            $qty = intval($qty);
            /**
             * Adding stock data to quote item
             */
            $result->setItemQty($qty);
            $qty = $this->getNumber($qty);
            $origQty = intval($origQty);
            $result->setOrigQty($origQty);
        }

In legacy implementation
\Magento\CatalogInventory\Model\StockStateProvider::checkQuoteItemQty

This case is not covered in MSI

[OlgaBurtyka]

I did some changes in commit, which allow save decimal qty_increment in configuration. But it's not all. There in many places exist issue regarding decimal. For example on admin in product page we can save decimal increment, but if one edit product page after re-save we will 0 in field(qty_increment);