[UR] Loader prefilter negative filters behave unexpectedly.

[aarongreig]

Right now we have some code in the loader which parses ONEAPI_DEVICE_SELECTOR to exclude loading libraries based on the backend components of the filter strings. The intention of this is that you can pass ONEAPI_DEVICE_SELECTOR=opencl:* and the loader will only load the opencl adapter library, which is beneficial because some adapter libraries have side-effects when loaded due to how drivers are implemented.

This code also supports negative filter strings, where you prepend ! to make your filter an anti-pattern. This can cause some strange behaviour because the device type component of the filters is completely ignored. For example, the filter string !opencl:fpga should mean "give me any device that doesn't have the opencl backend and the fpga device type", but our implementation interprets it as !opencl:*, or "give me any device that doesn't have the opencl backend" - which results in the opencl adapter not being loaded and no opencl devices being reported. A worse example is device type only filters: something like !*:cpu should mean "exclude cpu devices", but since the device type is ignored it becomes !*:* - exclude all devices, which results in none of the adapter libraries being loaded.