[4.x] When updating asset references, check the type of the data instead of max_files

[duncanmcclean]

This pull request attempts to prevent an issue where renaming / moving assets would cause the references to that asset in content to not be updated.

From my testing, a foreach() argument must be of type array|object, string given error would occur when a blueprint had an Assets field but the paths to the assets in the content was formatted differently.

For example:

• If you have max_files: 1 set on your Assets field, then later remove it, when you rename/move an asset, you'd experience the error because the AssetReferenceUpdater expects data to be stored as an array, however some data is still stored as strings.
• The reverse of this is also true. If you don't have max_files set at all, then set max_files: 1, when you rename/move assets, you'd experience the error since AssetReferenceUpdater expects the data to be an array but it's a string.

Closes #9701.
Related to #7555 and #8114.

[jesseleite]

Closing in favour of #9878. Thanks for taking the time to PR this! ❤️