Strip tags in schema values

Problem/Motivation

When using tokens as schema values, the value is filled as is, containing tags if the referenced token is a rich text field.

It must have a strip tags step before displaying the value on schema. This is similar to the metatags module.

Steps to reproduce

- Use a token in a schema referencing to a rich text field.
- The displayed schema will contain tags.

Proposed resolution

Strip tags before setting the schema value.