[SYCL][Doc][RTC] Add device global queries to kernel_compiler extension

[jopperm]

Adds three new methods on kernel_bundle to interact with device globals defined in runtime-compiled code:

bool ext_oneapi_has_device_global(const std::string &name);
void *ext_oneapi_get_device_global_address(const std::string &name, const device &dev); // return a device USM pointer suitable for queue::memcpy etc.
size_t ext_oneapi_get_device_global_size(const std::string &name);