Added fix for bug #11856

https://bugzilla.xamarin.com/show_bug.cgi?id=11856

This works for expressions by doing the following:
- it looks if the expression is the first in a sequence of conditional expressions
- if is first, it extracts all expressions in the chained expressions
- after that it compares all expressions and if two are found as duplicates, the first duplicate is shown

The code fix will remove the duplicate expression.

This bug will also look to bit operations ( & and | ) as they have similar semantics