[Remote Config] User can enter invalid characters into value fields

When configuring rules, if the user chooses a type limited by input such as an Int or Float, the value field will prevent the user from entering alphabetic characters, but not prevent symbols from being entered. This is then properly sanitised when pushing/pulling, however what the user will see is no longer synchronised the pushed data and they may not be aware of a erroneous value being submitted.

Steps to reproduce:
- Create and open a new project in Unity 2019.3 (+) or download the attached project
- If in a new project, install the Remote Config package via Package Manager (it may be a preview package)
- Window > Remote Config Management
- Under any environment, add a new rule ("Add Rule") and configure it as an Int type value
- In the value field, enter numeric characters, observing they are accepted
- In the value field, enter alphabetic characters, observing they are blocked
- In the value field, enter other symbolic characters ($%^&*@!), observing they are accepted though they do not represent a valid Int value
- "Push" the values, observing it appears to have pushed with no issues
- Observe the value field set previously still reflects the same value
- "Pull" values back from the server, observing the actual sanitised value now appears in the field