[Backport 2.3] Add swatch option: Prevent loosing data and default value if data is not populated via adminhtml

[gomencal]

Add swatch option: Prevent loosing data and default value if data is not populated via adminhtml.

Description

Adapt \Magento\Swatches\Model\Plugin\EavAttribute::setProperOptionsArray to make possible that the plugins afterSave in the same module doesn't delete data if they don't found this data with all the options data, as sent via adminhtml form.

Fixed Issues (if relevant)

1. Create attribute option via API for swatch attribute fails #10707: Create attribute option via API for swatch attribute fails
2. Can't import attribute option over API if option is 'visual swatch' #10737: Can't import attribute option over API if option is 'visual swatch'
3. Unable to add new options to swatch attribute #11032: Unable to add new options to swatch attribute
4. Impossible to add swatch options via Service Contracts if there is no existing swatch option for attribute #9410: Impossible to add swatch options via Service Contracts if there is no existing swatch option for attribute

Manual testing scenarios

1. Create a select attribute
2. Make this attribute use visual or text swatch
3. Try adding attribute options through the API via POST /V1/products/attributes/{attributeCode}/options

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)

[vkublytskyi]

@gomencal Your tests in #12036 look good. May I ask you to port them to 2.3-develop as well. You may not port them to 2.1-develop if you have no time but it is highly desirable to be sure that after 2.3 release we will not have test coverage degradation.