Ticket #830: refactoring functions in request API builder

Add a static function to gather the code present in "SetReadValueFromStrings" and "SetReadValue" functions (ReadRequest).

Then update these two previous functions with a new compact code : this is for testability and maintainability.

Similarly, in the same file with other function such as : BrowseRequest, WriteRequest...

See the good first issue : #830 (closed)