[UR] Investigate and deprecate `UR_DEVICE_TYPE_ALL`

[isaacault]

UR_DEVICE_TYPE_ALL doesn't fit properly with the use of the device_types enum. In most instances, vectors of device types are handled and edge cases are written into the code to support UR_DEVICE_TYPE_ALL.

For example, see

llvm/unified-runtime/source/loader/ur_adapter_registry.hpp

Lines 64 to 67 in d865c0c

	// If the adapter can report all device types then it matches.
	if (std::find(manifest.device_types.begin(), manifest.device_types.end(),
	UR_DEVICE_TYPE_ALL) != manifest.device_types.end()) {
	return true;

.

This has implications in the instance where this enum is extended for further device types. The use of this throughout should be investigated and if possible, deprecated in favor of vectors containing explicit device types.

[isaacault]

The example above was removed with bf20e6e. With that, the uses seem safe and removal would be costly at the moment. I propose improving the documentation to clarify when this value can and can't be used, as implemented in #17629 .