[C#] Fix nested structs and arrays in Object API (#5765)

[C#] Fix nested structs and arrays in Object API (#5765)

* [C#] Fix nested structs and arrays in Object API

The adds support for nested structs and fixed size arrays in the C#
Object API codegen which previously generated invalid code that wouldn't
compile.

- Nested structs would originally generate syntax errors due to adding an
  additional `.` to separate fields.
- Fixed size arrays of nested structs would originally generate code for
  the first field in the top most struct, and would lead to a compiler
  error due to referencing undefined variables.

* [C#] fix nested structs and arrays of structs.

* fix nested structs + arrays

* add table support

* Cleanup code

Co-authored-by: mugisoba <mugisoba+github@icloud.com>