[SYCL][DOC] Add sycl_ext_oneapi_enqueue_functions (#11491)

Adds a new extension proposal to simplify enqueuing work to a device.

- Uses different function names for different use-cases.
- Uses free-functions instead of member functions.
- Requires developers to opt-in to the creation of event objects.

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Signed-off-by: John Pennycook <[email protected]>
Co-authored-by: Ben Ashbaugh <[email protected]>
Co-authored-by: Greg Lueck <[email protected]>

Author: 3 people