CppTools: remove ambiguity in Usages class name

Usages class is used in findUsages and globalRename in further changes.

Change-Id: I2f314e4ebe7828e59fcc3cae824893c96eb21cab
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/cpptools/cpptools.pro

@@ -95,6 +95,7 @@ HEADERS += \
     cppsymbolinfo.h \
     cursorineditor.h \
     wrappablelineedit.h \
+    usages.h
 
 SOURCES += \
     abstracteditorsupport.cpp \

src/plugins/cpptools/cpptools.qbs

@@ -203,6 +203,7 @@ Project {
             "symbolsfindfilter.h",
             "typehierarchybuilder.cpp",
             "typehierarchybuilder.h",
+            "usages.h"
         ]
 
         Group {