add math functions for complex type for the oneAPI backend

[AuroraPerego]

The oneAPI backend did not have the specialization of math functions on the device for complex types.
I moved (to avoid code duplication) the specializations done for CUDA/HIP to Complex.hpp to allow the oneAPI backend to use them as well.

[AuroraPerego]

This failure in the tests with windows does not seem related to the PR:

+++ choco uninstall cmake.install
Chocolatey v2.4.0
Uninstalling the following packages:
cmake.install

cmake.install v3.31.1
 Running auto uninstaller...
 [AutoUninstaller] The installation source for this product is not available. Verify that the source exists and that you can access it.
 [AutoUninstaller] 
 [AutoUninstaller] 
 Auto uninstaller failed. Please remove machine installation manually.
 Exit code was 1612
 cmake.install has been successfully uninstalled.

Chocolatey uninstalled 1/1 packages. 
 See the log for details (C:\ProgramData\chocolatey\logs\chocolatey.log).

Warnings:
 - cmake.install -  Auto uninstaller failed. Please remove machine installation manually.
 Exit code was 1612