Globally replace 'base_contains' calls with 'bb.utils.contains'

The base_contains is kept as a compatibility method and we ought to
not use it in OE-Core so we can remove it from base metadata in
future.

(From yocto-docs rev: b8e7dee82929213e7581d6c598f42da74ee03988)

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/ref-classes.xml

@@ -3211,7 +3211,7 @@
         The <filename>utils</filename> class provides some useful Python
         functions that are typically used in inline Python expressions
         (e.g. <filename>${@...}</filename>).
-        One example use is for <filename>base_contains()</filename>.
+        One example use is for <filename>bb.utils.contains()</filename>.
     </para>
 
     <para>