[SYCL][RTC] Initial support for device globals

[jopperm]

Adds limited support for device globals in runtime-compiled SYCL code. The application interacts with the globals via three new methods on kernel_bundle:

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 USM pointer suitable for queue::memcpy etc.
size_t ext_oneapi_get_device_global_size(const std::string &name);

This PR uses the same trick as #16316, i.e. prepending a kernel-bundle-specific prefix to the names of device globals to make them distinguishable for the program manager.

Limitations:

• Device globals inside a namespace are unsupported due to insufficient name mangling.
• Device globals with the device_image_scope property cannot be read/written from the host, because the runtime currently cannot expose USM pointers for them. A workaround is using explicit kernels to read/write the global's value into a USM buffer.

[jopperm]

Implementation (here) and specification draft (#17401) are up-to-date.

[sommerlukas]

Just one question, rest LGTM.

[sommerlukas]

Do we currently check this part?

only true if kernel_bundle was created from source

Would that enable an early return, avoiding the linear search?

[jopperm]

A non-RTC bundle would just have an empty list of names, so the linear search isn't really a problem, but we can at least detect that before doing the string operations (and map lookups in case of kernels); see 1be7568.