Allow "@tag" and "@filter" directives to appear together

[obi1kenobi]

Currently, using @tag and @filter on the same property field is disallowed for the sake of implementation simplicity.

However, there are legitimate use cases that would benefit from this ability – especially in situations such as field_name @tag(tag_name: "my_tag") @filter(op_name: "!=", value: ["%another_tag"]) where it is impossible to work around this limitation.

[obi1kenobi]

Relevant bit of code, from current master: https://github.com/kensho-technologies/graphql-compiler/blob/1fdbbf8b9763a4f169daef0625e7898ff13e471d/graphql_compiler/compiler/compiler_frontend.py#L431