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Re-order OrderByIdem parser to proceed with SimpleArithmetic expressions before functions

• The subject line should be less than 50 chars, you can and should use the commit message body if you need more; in fact, the great explanation you put in your first Github message should go there.
• OrderByIdem => OrderByItem

Here is how it could look like:

Parse simple arithmetic expressions before functions

There is parser bug for OrderByItem(), where a function is detected
before a SimpleArithmeticExpression while it should be the reverse:
simple arithmetic expressions can start with a function too, and thus
they should be matched first if present.

This fix enables the use of expressions in sorting and with window
functions.

Thanks @greg0ire for your feedback, they should now all be resolved