[NFC] Add ImportProcessor class & unit tests + extend existing cover

[eileenmcnaughton]

Overview

Adds a bunch of helpers which will allow us to massively cleanup loadSavedMapping and add test cover. This change is NFC of itself as it does not start to USE the new helpers as yet. The goal is to bring in the usage alongside tests of the live code

Before

Currently to get the value for 'type' the code looks like

          list($mappingName, $mappingContactType, $mappingLocation, $mappingPhoneType, 
        $mappingImProvider, $mappingRelation, $mappingOperator, $mappingValue, 
    $mappingWebsiteType) = CRM_Core_BAO_Mapping::getMappingFields($savedMapping, TRUE);

            $locationId = isset($mappingLocation[$i]) ? $mappingLocation[$i] : 0;
            $phoneType = isset($mappingPhoneType[$i]) ? $mappingPhoneType[$i] : NULL;
            // default for IM/phone when mapping with relation is true
            $typeId = NULL;
            if (isset($phoneType)) {
              $typeId = $phoneType;
            }
            elseif (isset($imProvider)) {
              $typeId = $imProvider;
            }

After

we can replace the above with

$type = $processor->getPhoneOrIMTypeID($i);

Similar applies to all the other hard-to-read code. We are really just doing a fairly simple mapping conversion & it doesn't need to be so hard.

Also the CRM_Core_BAO_Mapping::getMappingFields function will be close to obsolete once this has been adopted

Technical Details

This adds the full ImportProcessor class from the WIP pr #15034 - minus the functions that
replace loadSavedMapping) along with tests. It does NOT start to use the new class as yet.

Comments

Note that #15068 will need rebasing if this is merged first & vice versa

The goal is to bring this class into use along with extending tests but this is 'safe' in that no functional code is changed

[civibot]

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[eileenmcnaughton]

@totten @demeritcowboy @seamuslee001 so what was the decision on this one?

[seamuslee001]

Seems fine to me, Code in the import processor isn't fully live yet and it adds tests merging