[container.requirements.general] Move exposition-only concept

The exposition-only concept container-compatible-range is defined
in the subclause for allocator-aware containers, that does not
actually use it.  This requirement is used throughout the subclause
for a variety of contains, so relocate the definition into the
leading subclause that provides a key to definitions used throughout
the containers subclauses.

Author: morinmorin

source/containers.tex

@@ -95,6 +95,14 @@
 \tcode{rv} denotes a non-const rvalue of type \tcode{X}.
 \end{itemize}
 
+\pnum
+The following exposition-only concept is used in the definition of containers:
+\begin{codeblock}
+template<class R, class T>
+concept @\defexposconcept{container-compatible-range}@ =    // \expos
+  ranges::@\libconcept{input_range}@<R> && @\libconcept{convertible_to}@<ranges::range_reference_t<R>, T>;
+\end{codeblock}
+
 \rSec3[container.reqmts]{Containers}
 
 % Local command to index names as members of all containers.
@@ -951,14 +959,6 @@
 but specialized allocators can choose a different definition.
 \end{note}
 
-\pnum
-The following exposition-only concept is used in the definition of containers:
-\begin{codeblock}
-template<class R, class T>
-concept @\defexposconcept{container-compatible-range}@ =    // \expos
-  ranges::@\libconcept{input_range}@<R> && @\libconcept{convertible_to}@<ranges::range_reference_t<R>, T>;
-\end{codeblock}
-
 \pnum
 In this subclause,
 \begin{itemize}