Use ptr from mmap for GHistIndexMatrix and ColumnMatrix. (#9315)

* Use ptr from mmap for `GHistIndexMatrix` and `ColumnMatrix`.

- Define a resource for holding various types of memory pointers.
- Define ref vector for holding resources.
- Swap the underlying resources for GHist and ColumnM.
- Add documentation for current status.
- s390x support is removed. It should work if you can compile XGBoost, all the old workaround code does is to get GCC to compile.

doc/tutorials/dask.rst

@@ -54,6 +54,9 @@ on a dask cluster:
         y = da.random.random(size=(num_obs, 1), chunks=(1000, 1))
 
         dtrain = xgb.dask.DaskDMatrix(client, X, y)
+        # or
+        # dtrain = xgb.dask.DaskQuantileDMatrix(client, X, y)
+        # `DaskQuantileDMatrix` is available for the `hist` and `gpu_hist` tree method.
 
         output = xgb.dask.train(
             client,