Use `wp_kses_data` for validating text fields

Use ```wp_kses_data``` over ```wp_filter_kses``` for validating text fields - does the same, but will not slash escape the data.

Issue:
```scbForms::validate_post_data()``` strips the slashes from posted values, but in ```scbTextField::validate()``` they are added back by ```wp_filter_kses```.