Add common validators to shared tools

[hartsick]

There are a number of validators I find us referencing in GCF on CMR, that I was wondering if we should try to abstract a little and pull into the styleguide for shared usage across teams.

In my mind, these would represent some best practices for validation.

Below are some examples that are top of mind for me:

• Email format (current GCF, reused in CMR)
• Phone format (length in GCF, Twilio validation in GCF, non-Twilio length and format in CMR)
• Date—this would be used for our new MM/DD/YYYY free text date input (current GCF - specific to birthdays, current CMR [optional, required])

There are a lot of others in GCF that we might assess for usefulness in different contexts, too