[meta.reflection.array] Replace "Constant When" with "Throws"

Author: Eisenwave

source/meta.tex

@@ -5896,11 +5896,6 @@
 \pnum
 Let \tcode{T} be \tcode{ranges::range_value_t<R>}.
 
-\pnum
-\constantwhen
-\tcode{reflect_constant(e)} is a constant subexpression
-for every element \tcode{e} of \tcode{r}.
-
 \pnum
 \mandates
 \tcode{T} is a structural type\iref{temp.param},
@@ -5931,6 +5926,12 @@
 \returns
 \tcode{\reflexpr{$P$}}.
 
+\pnum
+\throws
+\tcode{meta::exception} unless
+\tcode{reflect_constant(e)} is a constant subexpression
+for every element \tcode{e} of \tcode{r}.
+
 \pnum
 \begin{note}
 $P$ is a potentially non-unique object\iref{intro.object}.