Prevent hard error when a string is too long for a field.

Prevent hard error when a string is too long for a field.

Over time we have had various requests to extend the length of various
fields (currently https://github.com/civicrm/civicrm-core/pull/12939 ).

The main issue is not that it matters to capture every single character of
a crazy long user entered field - but that a hard fail when the data is too long can lose payment or registration or other data & provide a bad
experience.

This PR makes it still save, with a logged message & the utf friendly
function in play. As of writing the api validation is stilltight - see
```
  // Check our field length
    throw new API_Exception("Value for $fieldName is " . strlen(utf8_decode($value)) . " characters  - This field has a maxlength of {$fieldInfo['maxlength']} characters.",
      2100, array('field' => $fieldName)
    );
  }
```
and changing this is up for discussion.

Note that at the UI level max field lengths can be enforced by using
addField which uses metadata to determine field length etc