[ESIMD] Refactor simd vector element type traits infra. (#6655)

* [ESIMD] Refactor simd vector element type traits infra.

These changes make the type traits infrastructure significantly better
structured, more readable, more suitable for addition of a new wrapper
type. Particularly:
- no cyclic dependence between elem_type_traits.hpp and types.hpp any
  more, which protects against hard to solve template instantiation
  errors
- move traits implementation for sycl::half into a separate header,
  now elem_type_traits.hpp don't depend on any specific wrapper type, it
  only provides generic infra
- improve "traits" model - now __esimd* "intrinsics" which implement
  conversions and operations are replaced with *traits structures
  templated on the wrapper type, operation and number of elements. This
  allows partial specializations and makes it easy to identify what
  needs to be done to implement new wrapper type (implement *traits
  specializations)
- create a new types_elementary.hpp as a container for basic definitions
  not depending on the rest of ESIMD
- remove dependence of is_wrapper_elem_type_v on specific types.

Signed-off-by: Konstantin S Bobrovsky <konstantin.s.bobrovsky@intel.com>

Author: kbobrovs

sycl/include/sycl/ext/intel/esimd.hpp

@@ -81,6 +81,7 @@
 
 #include <sycl/ext/intel/esimd/alt_ui.hpp>
 #include <sycl/ext/intel/esimd/common.hpp>
+#include <sycl/ext/intel/esimd/detail/half_type_traits.hpp>
 #include <sycl/ext/intel/esimd/simd.hpp>
 #include <sycl/ext/intel/esimd/simd_view.hpp>
 #include <sycl/ext/intel/experimental/esimd/kernel_properties.hpp>