Added RowBuilder widget documentation

[serhiyzhovnir]

Purpose of this pull request

This pull request (PR) adds documentation about the RowBuilder widget.

Affected DevDocs pages

This documentation will have the following links:

• https://devdocs.magento.com/guides/v2.2/javascript-dev-guide/widgets/widget-row-builder.html
• https://devdocs.magento.com/guides/v2.2/javascript-dev-guide/widgets/widget-row-builder.html

Page look:

Links to Magento source code

• https://github.com/magento/magento2/blob/2.3/app/code/Magento/Theme/view/frontend/web/js/row-builder.js#L25
• https://github.com/magento/magento2/blob/2.2/app/code/Magento/Theme/view/frontend/web/js/row-builder.js#L25
• https://github.com/magento/magento2/blob/2.2/app/code/Magento/SendFriend/view/frontend/templates/send.phtml#L47
• https://github.com/magento/magento2/blob/2.3/app/code/Magento/SendFriend/view/frontend/templates/send.phtml#L47

whatsnew
Added a new topic about the RowBuilder widget.

[devops-devdocs]

An admin must run tests on this PR before it can be merged.

[rogyar]

Hi @serhiyzhovnir. Thank you for the great topic. Please, perform a few minor adjustments and we are good to go.

[serhiyzhovnir]

Hi @rogyar
The PR was adjusted. Please, review it again.
Thank you!

[jeff-matthews]

Thanks for the new topic @serhiyzhovnir! I made some minor editorial suggestions.

[serhiyzhovnir]

Hi @jeff-matthews
The PR was adjusted.
Thank you!

[jeff-matthews]

Thanks @serhiyzhovnir!

[jeff-matthews]

@serhiyzhovnir, I just noticed some markdown syntax errors in your branch that will fail tests. Please fix these issues so I can finish processing:

 rake test:cicd
Testing Markdown style with mdl ...
guides/v2.2/javascript-dev-guide/widgets/widget-row-builder.md:44: MD009 Trailing spaces
guides/v2.3/javascript-dev-guide/widgets/widget-row-builder.md:44: MD009 Trailing spaces

A detailed description of the rules is available at https://github.com/markdownlint/markdownlint/blob/master/docs/RULES.md

The Markdown linter has found 4 issues

[serhiyzhovnir]

Hi @jeff-matthews
The trailing spaces were removed.
Please, check the PR again.
Thank you!

[jeff-matthews]

Confirmed. Thanks @serhiyzhovnir!

[jeff-matthews]

running tests

[ghost]

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