magento/magento2#80862 Custom Product Attribute changes backend_type property

[keyurshah070]

Description

Fixed Issues (if relevant)

1. Custom Product Attribute changes 'backend_type' when 'is_user_defined = 1' and get updated/saved in Admin Backend #9219: Custom Product Attribute changes 'backend_type' when 'is_user_defined = 1' and get updated/saved in Admin Backend
2. User define product attribute backend type change from backend save.
3. So if we have backend type as varchar(on Installer script) with its value in a string and after creating attribute when we update its property from backend then it changes backend type to integer. so we cannot save its attribute value on a product level

Manual testing scenarios

1. Created Installer script with backendtype as varchar and change its property from backend and after saving attribute still, I have backendtype as varchar

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)

[omiroshnichenko]

Hi, @keyurshah070. Could you please verify failed tests. Also you have opened concurrent PR #11837 that will have conflict with current. Can you, please, let us know if you would continue working on it or we should close it. Thank you.