[flang] Classify IEEE_ARITHMETIC elemental functions and operators as SIMPLE (#223254)
Fortran 2023 17.11.1 paragraph 1 specifies the `IEEE_ARITHMETIC` module
functions as `SIMPLE`, and 17.2 paragraph 3 specifies the elemental `==`
and `/=` operators for `ieee_class_type` and `ieee_round_type` as
`SIMPLE`.
This change:
- Classifies the `IEEE_ARITHMETIC` elemental functions as `SIMPLE`
- Classifies the elemental `==` and `/=` operators for `ieee_class_type`
and `ieee_round_type` as `SIMPLE`
- Adds tests to verify the `SIMPLE` attributes
Part of the `SIMPLE` procedure support tracked in #221457.