Since SYCL 2020 no longer has the SYCL 1.2.1 images, neither the
`device::info::image_support` query nor `aspect::image` query guarantees
that a given device support the SYCL 1.2.1 images. To alleviate this,
this commit adds an extension with a new aspect `ext_intel_legacy_image`
intended for querying support for SYCL 1.2.1 images.

To help users correctly transition to using this new aspect, a warning
is issued when the user calls either `platform::has` or `device::has`
with `aspect::image`, warning the user that SYCL 2020 images are not
supported and suggesting they use the new aspect instead. In a future
update, these calls will be changed to return false due to missing
SYCL 2020 image support.

Signed-off-by: Larsen, Steffen <steffen.larsen@intel.com>

Signed-off-by: Larsen, Steffen <steffen.larsen@intel.com>

Signed-off-by: Larsen, Steffen <steffen.larsen@intel.com>

…spect