Make idl_parser deterministic (#6976)
Make idl_parser deterministic (#6976)

* Make idl_parser deterministic

Some golden tests even exercise this [logic](https://github.com/google/flatbuffers/blob/df2df21ec1be2468106fed10c1533eacc1cf0d2e/tests/prototest/test.golden#L8). Let's make the parser fully stable not depending on the implementation of std::sort

* Retry the ci
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