[Forwardport] Fix to allow use decimals less then 1 in subproducts qty.

[ihor-sviziev]

Original Pull Request

#14752

Quick fix to allow use decimals less then 1 in subproducts qty.

The same as #14693 but from fork.

Description

There is impossible to place order from grouped product where subproducts qty less then one.

Fixed Issues (if relevant)

1. 'validate-grouped-qty' validation is meaningless #14692: 'validate-grouped-qty' validation is meaningless

Manual testing scenarios

1. Set "Qty Uses Decimals" = Yes and Minimum Qty Allowed in Shopping Cart" = 0.01 for all products on any grouped product.
2. Go to groped product page on frontend.
3. Put for all suproducts qty less than 1.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @ihor-sviziev. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.3.0 release.