Pulling in latest changes from VVL
Use BUILD_TESTS instead of VUL_TESTS. While it's good practice to
prefix variable names it makes updating this code more difficult.
Also since tests can only ever be enabled if the project is top
level, it doesn't affect add_subdirectory users.
Other misc. CMake cleanup
Allows build options specific to Vulkan-Utility-Libraries to be
easily grouped via cmake-gui.
This approach is also nicer for users who consume the library via
add_subdirectory or FetchContent since it more obvious what
settings are being ovverriden.
Remove UTILITY_LIBRARIES_CPP_STANDARD since we don't have a
reason to support multiple CPP standards.
Set testing to OFF by default to make consuming the library easier
for users and package managers.
