[SYCL][DOC] Expand complex extension with complex support for sycl::marray (#11792)

This PR is the updated version of the "complex support for sycl::marray"
extension, which used to be a separate extension.
However, after discussing whether it should be a separate extension
versus an expansion (#8852), the
complex expansion has been decided.

Following the proposal for `sycl::ext::oneapi::experimental::complex`
which adds the support of complex for SYCL, this expansion proposes to
incorporate complex support for `sycl::marray` and new complex math
features.

Implementation: #8647

Author: jle-quel