[container.requirements] Improve index entries for contiguous and reversible containers. (#4051)

Author: Eelis

source/containers.tex

@@ -366,10 +366,11 @@
 swap.
 
 \pnum
+\indextext{reversible container|see{container, reversible}}%
 If the iterator type of a container belongs to the bidirectional or
 random access iterator categories\iref{iterator.requirements},
 the container is called
-\term{reversible}
+\defnx{reversible}{container!reversible}
 and meets the additional requirements
 in \tref{container.rev.req}.
 
@@ -465,8 +466,7 @@
 within that container.
 
 \pnum
-\indextext{container!contiguous}%
-A \defn{contiguous container}
+A \defnadj{contiguous}{container}
 is a container
 whose member types \tcode{iterator} and \tcode{const_iterator}
 meet the