Generalize prediction cache. (#8783)

* Extract most of the functionality into `DMatrixCache`.
* Move API entry to independent file to reduce dependency on `predictor.h` file.
* Add test.

---------

Co-authored-by: Philip Hyunsu Cho <chohyu01@cs.washington.edu>

src/data/data.cc

@@ -10,6 +10,7 @@
 #include <cstring>
 
 #include "../collective/communicator-inl.h"
+#include "../common/api_entry.h"  // XGBAPIThreadLocalEntry
 #include "../common/group_data.h"
 #include "../common/io.h"
 #include "../common/linalg_op.h"