81892b20 "loplugin:unnecessaryparen when
compiling as C++17, so the ParenExpr is no longer hidden behind
ExprWithCleanups/CXXConstructExpr/MaterializedTemporaryExpr wrappers" gave me
the idea to generally look though IgnoreImplicit instead of IngoreImpCasts in
loplugin:unnecessaryparen.  However, that would still not look through implicit
CXXConstructExpr, so would still not have found the occurrences in
81892b20 when compiling in pre-C++17 mode.
Therefore, let ignoreAllImplicit also look through CXXConstructExpr.  (I am not
entirely sure in which situations non-implicit CXXConstructExpr---that should
thus not be ignored---would occur, but assume they would be underneath something
like a CXXFunctionalCastExpr, which is not ignored.)

Change-Id: I947d08742e1809150ecc34a7abe84cca5e0ce843