5.3 - Handle 'Check for Matching Contact(s)' button with ajax

[colemanw]

Overview

Fixes the 'Check for Matching Contact(s)' button when ajax deduping is enabled

Before

The button would still work if ajax deduping was disabled in system prefs, but didn't work if ajax mode is enabled.

After

The button works either way. If ajax mode is enabled, clicking the button will use ajax. Otherwise it does it the old way.

[civibot]

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[seamuslee001]

As per my comment here #12547 (comment) i tested this on a 5.3 install and it passed ping @eileenmcnaughton @monishdeb @totten

[colemanw]

FYI Unit tests don't cover .tpl files, so the pending PR tests are irrelevant.

[colemanw]

Whoops, I just had a little git mistake and when updating this PR I accidentally pushed to the civicrm repo instead of my branch. So commit 116f2b4 is now in the 5.3 branch. But this PR still needs to be merged to get the other commit.