Unique field names handling needs to be improved(?)

[eri-trabiccolo]

Reproduction Steps

• Edit a form and create a field, using the hame "whatever"
• Turn it to a reusable block and save it
• Create or edit another form and add the reusable block just created
• turn the reusable block into a normal block
• Alter the label, the description, whatever (but not the name)
• save the form

Expected Behavior

• I'd expect to not be able to save the field, which is not a reusable field anymore, because it has a non unique name

Actual Behavior

• I can save the form with the field that has a non unique name

Error Messages / Logs

n/a

System and Environment Information

dafd798

###This issue has be recreated:

• Locally
• On a staging site
• On a production website
• With only LifterLMS and a default theme

Browser, Device, and Operating System Information

n/a

[thomasplevy]

This is nearly identical to #104 but not exactly. It's all interrelated in that our automatically generated values / validation isn't working right in these scenarios.