Doc: Add alternative terms for "shadow build" to the glossary

Change-Id: I36e160840520778f5ef7012ef72fb1abb967a3c5
Reviewed-by: Jörg Bornemann <joerg.bornemann@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

doc/qtcreator/src/overview/creator-only/creator-glossary.qdoc

@@ -125,6 +125,10 @@
                 if you need many build configurations for a single set of
                 source files.
 
+                Shadow builds are also widely known as \e {out-of-source builds}
+                to separate them from \e {in-source builds} or
+                \e {in-tree builds}.
+
     \endtable
 
 */