Add regex and length validation to all text-based elements

Problem/Motivation

The module doesn't fully pass to formkit the validation for text fields' length.

Additionally, when a regex is added, the validation is overridden because the regex logic creates a formkit "string" validation rather than array.

Proposed resolution

I attach here my proposed solution:

• Length checks are added for TextField and TextAreaField
• Regex validation is moved to a separate function, returns an array to be concatenated with previous validations.
• Regex validation function also returns the validation message set in webform.