[Kernel] add support of build databases to -json-compilation-database

src/kernel_services/ast_queries/json_compilation_database.ml

tests/jcdb/build_commands.json

tests/jcdb/jbdb.c

tests/jcdb/jbdb2.c

tests/jcdb/oracle/jbdb.res.oracle

tests/jcdb/oracle/jbdb2.res.oracle