Native Angular forms validation support

[nfellinger]

It would be desirable to have native support for Angular reactive and template-driven forms validation to make use of the validation messages and styling which DB-UX provides for input elements.
Currently components like db-input only support standard html validation with attributes like required or min/max etc..

Validators of Angular formControls that are bound to db-input (or any other DB-UX data input element) are ignored forcing developers to implement their own custom implementation of input validation messages.

This would also provide an opertunity to extend the functionality of one simple validation message to support multiple validation messages per element. Since formControls can have multiple validation errors, a possible usage scenario could look something like this:

<db-input formControlName="username" label="Username">
    <db-infotext error="usernameRequired">A username is required</db-infotext>
    <db-infotext error="usernameTooLong">Max length of username is 100</db-infotext>
    <db-infotext error="usernameAlreadyExists">This username is already taken</db-infotext>
</db-input>

[LSchroff]

Jira 4511