Ensures migration properly converts multiple individual entity embeds within a single text field value

This changes the regex for matching the tags in the field value to be non-greedy. The previous regex would end up matching EVERYTHING between the first opening tag and the last closing one. If there were multiple embedded entities, this would cause broken code that could not be displayed correctly. It might appear that only one of the embed tags was converted, but if there was also text content in between the embeds then that would also not be rendered properly.

Making the regex non-greedy ensures that it matches each individual entity embed tag, thus properly converting all of them without breaking the code.

Closes #3491721