Fixes a bug where the logic to determine when to use a C# enum flags
both enums and vectors of enums. This causes the C# generator to
generate code that doesn't compile for tables that contain vectors of
enums.
The fix also consolidates type generation functions a bit and adds
some additional casting functions for clarity.
When creating a CreateXxx(...) method for a simple table type,
enum-type fields with a non-zero default must have an explicit
cast for the respective argument default value, because in C#,
there is an implicit cast from int to an enum only for 0.
Also, added an example of such type into the example monster_test
type, so that we test this feature.
Donnell