[L0] Building hashtable on GPU

[akroviakov]

The code in this branch is supposed to link into separately built shared library and currently represents the HDK side of talking to a shared library. The current (ugly) workflow to test this is as follows:

1. Get a separate conda env with dpcpp-cpp-rt
2. Activate it, build shared library and add the path to where to look for the .so to the respective find_library() call in cmake, modify the path for the header in BaselineHashTableBuilder.h and for Perfect Hash respectively.
3. Build HDK with omnisci-dev
4. Run tests using conda env from step 1

Currently passes JoinHashTableTest