dev/core#1123 - avoid possible variable name clash

[demeritcowboy]

Overview

As per the comment at #15147 (comment) this avoids a possible smarty variable name clash with files that might get {include}'d, especially for custom activity types that have their custom templates automatically included. The variable name 'activityType' might be too common.

Comments

Putting against 5.18 because I meant to get to it earlier but was too slow and it got branched before I got to it.

[civibot]

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[eileenmcnaughton]

OK - but sigh. The other made more sense but i see your reasoning