never build or install libze_loader

[bratpiorka]

In any case, we should never build or install libze_loader.

Currently, when the user enables the Level Zero Memory Provider, only the 'ze_api.h' header is required for building.
If the user sets the UMF_LEVEL_ZERO_INCLUDE_DIR, the header is taken from this location.
If not, Level Zero is fetched, built, and added to the make-install targets, which is incorrect.

Moreover, the libze_loader library should be used only in GPU tests, benchmarks, and examples.
This library should never be built by UMF.

The fix should:

• use UMF_LEVEL_ZERO_INCLUDE_DIR as the primary source for obtaining 'ze_api.h'

• if this variable is not set, Level Zero should be located using CMake's find_package()

• only then should the Level Zero header be fetched from GitHub, but without calling FetchContent_MakeAvailable()

• introduce a new UMF_LEVEL_ZERO_LIB_DIR variable that should be checked for the libze_loader library.

• if this variable is not set, find_package() should attempt to locate Level Zero libraries (note: the workflows in UMF should utilize this).

Additionally, the behavior between Level Zero and CUDA should be consistent.

[bratpiorka]

@igchor @vinser52 please review this issue

[vinser52]

First, looks like the #1100 can be closed as a duplication of this issue. I think this one is more generic than the #1100.

Regarding what you captured:

• use UMF_LEVEL_ZERO_INCLUDE_DIR as the primary source for obtaining 'ze_api.h'

• only then should the Level Zero header be fetched from GitHub, but without calling FetchContent_MakeAvailable()

These bullets are related to the libumf.so build

• if this variable is not set, Level Zero should be located using CMake's find_package()

• introduce a new UMF_LEVEL_ZERO_LIB_DIR variable that should be checked for the libze_loader library.

• if this variable is not set, find_package() should attempt to locate Level Zero libraries (note: the workflows in UMF should utilize this).

And these are related to the tests, right?