CppEditor: Generalize CppUseSelectionsUpdater

Let CppUseSelectionsUpdater delegate the work to
*EditorDocumentProcessor so that the clang code model can also provide
results.

Change-Id: I6872afbfeea1a5c4a64fdf19fcb1992f134dde08
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/cpptools/cpptools.qbs

@@ -40,6 +40,8 @@ Project {
             "builtineditordocumentprocessor.h",
             "builtinindexingsupport.cpp",
             "builtinindexingsupport.h",
+            "builtincursorinfo.cpp",
+            "builtincursorinfo.h",
             "clangcompileroptionsbuilder.cpp",
             "clangcompileroptionsbuilder.h",
             "clangdiagnosticconfig.cpp",
@@ -81,6 +83,7 @@ Project {
             "cppcompletionassistprocessor.h",
             "cppcompletionassistprovider.cpp",
             "cppcompletionassistprovider.h",
+            "cppcursorinfo.h",
             "cppcurrentdocumentfilter.cpp",
             "cppcurrentdocumentfilter.h",
             "cppdoxygen.cpp",