Add a Process_printPercentage helper routine

Replace several open-coded variants of percentage formatting.
This function has been ported from Hishams old 'next' branch.

Process.h

@@ -356,6 +356,8 @@ void Process_fillStarttimeBuffer(Process* this);
 
 void Process_printLeftAlignedField(RichString* str, int attr, const char* content, unsigned int width);
 
+void Process_printPercentage(float val, char* buffer, int n, int* attr);
+
 void Process_display(const Object* cast, RichString* out);
 
 void Process_done(Process* this);