[obj.lifetime] Reinstate phrasing "aggregate type".

This wording is in the approved paper P3726R2 from CWG Motion 9,
but was changed editorially to just "aggregate" under the assumption
that "aggregate type" is not a defined term. However, this seems
misguided; we use both the terms "aggregate type" and "class type",
even though the defined terms are just "aggregate" and "class".
It seems generally to improve clarity to refer to a "type", and here
in particular as we are talking about an "implicit-lifetime type".

Addresses editorial review committee feedback.

Author: tkoeppe

source/memory.tex

@@ -1057,7 +1057,7 @@
 \pnum
 \mandates
 \tcode{T} is a complete type and
-an implicit-lifetime\iref{basic.types} aggregate\iref{dcl.init.aggr}.
+an implicit-lifetime\iref{basic.types} aggregate\iref{dcl.init.aggr} type.
 
 \pnum
 \effects