Added id to draft js editor field

[abotteram]

Summary

This PR can be summarized in the following changelog entry:

• Adds a fieldId prop in ReplacementVariableEditorStandalone, that gets added as an id attribute to the DraftJS editor element with the contenteditable attribute.

Relevant technical choices:

*

Test instructions

This PR can be tested by following these steps:

• Make sure this branch is checked out and yoast-components is linked to wordpress-seo.
• On the post edit page open the snippet editor.
• Inspect the source and look for the div with id snippet-editor-field-title. This was the existing id on the container wrapper.
• Now look for the div with id snippet-editor-field-title-field. This is the newly added id. Make sure the same div has the contenteditable attribute.
• The same can be done for snippet-editor-field-description and snippet-editor-field-title-field.

Fixes #637

[Dieterrr]

CR done 👍

[afercia]

I must assume the test instructions haven't been updated and this concern:

We can't rename the earlier id we introduced because of backwards compatibility. The snippet-editor-field-title part comes from a prop, so it can be changed if the developer that uses the component chooses too.

has since then been reconsidered. If so, please let me know and this can be merged 🙂 /Cc @Xyfi

[afercia]

Discussed internally and seems the ID renaming is not a concern.