CppTools: Extract ProjectPartChooser

...and put it under tests.

Change-Id: Id4bd2391abd1dfdc23640e871453558566cb0693
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/cpptools/cpptoolsunittestfiles.pri

@@ -18,7 +18,7 @@ HEADERS += \
     $$PWD/cppbaseprojectpartbuilder.h \
     $$PWD/projectinfo.h \
     $$PWD/cppprojectinterface.h \
-
+    $$PWD/cppprojectpartchooser.h \
 
 SOURCES += \
     $$PWD/cppprojectfile.cpp \
@@ -29,3 +29,4 @@ SOURCES += \
     $$PWD/clangcompileroptionsbuilder.cpp \
     $$PWD/cppbaseprojectpartbuilder.cpp \
     $$PWD/projectinfo.cpp \
+    $$PWD/cppprojectpartchooser.cpp \