* [idl_parser] Check structs and enums do not clash in a namespace
Uses fully qualified names to check for clashes within a given namespace whether explicitly defined or in the global namespace.
* [idl_parser] Move type name clash check to ParseEnum and ParseDecl
Change point at which parsing error is returned to ensure error is caught more generally. This change means that the error is returned after parsing the entirety of the offending duplicate rather than at the start when parsing it's name.
* [idl_parser] Add single and multi file type name clash tests
Adds a selection of tests for valid single file schemas with types that have the same name but are in different namespaces.
Adds a test for an a valid schema that spans two files with two types that have the same name but are in different namespaces.
Adds a test for an an invalid schema that spans two files with two types that have the same name and are in the same namespace.
Fraser Crossman