'fieldValues' should be a restricted handle in matrix blocks

[dmatthams]

Description

Had a table field within a matrix block with the handle 'fieldValues' which when attempting to loop via twig, caused an error stating I was attempting to loop a string – leading to much head scratching.

Steps to reproduce

1. Create a matrix block containing a table field (or any field it seems) with the handle 'fieldValues'
2. Attempt to loop through 'fieldValues' with twig

Additional info

• Craft version: 3.1.28
• PHP version: 7.0
• Database driver & version: MySQL

[brandonkelly]

Just added that for the next Craft 3.2 RC release.