refactor(operators): don't rely on operators extern var index

[FranckG28]

I've refactored operators.c to avoir using the extern var operators

• it was an extern var, and his name can be confusing in a lot of file where we are also defining operators var. This refactor avoid the creation of any global vars.
• operator detection was relying on the fact that the string in operators[] are in the same order as the operators enum. This can cause errors if we want to make changes to operators.
• removed is_operator function since we can check if the get_operator_type return UNKNOWN instead.

[jvondermarck]

Yessss that's a great observation ! Really good !