Form Builder - Clarify "Security" options

Form Builder - Clarify "Security" options

Follow-up to 54354d0430b2331bd8c80f1b5c868b2c668624f1, which was a small thing thrown into the bigger #24832

Before
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* Originally, "Security" options were labeled as "Role-Based" (RBAC) and "Form-Based" (FBAC)
    * This is confusing, because it packs a subtle distinction into two phrases which are slightly jargony.
* Currently, "Security" options are labeled as "Enforce Permissions" (RBAC) and "Open Access" (FBAC)
    * This is confusing, because "Open Access" wrongly suggests that the access is, well, open. (It's
      actually dependent on the overall configuration.)

After
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* Security is "User-Based" or "Form-Based"
* There is also a longer description.