Created by: xjqbest

• copy some feasigns and corresponding embeddings from one sparse table to another
• copy all feasigns and corresponding embeddings from one sparse table to another
• copy all dense params from one table to another
• copy some local vars to other local vars

usage: add the following config in fleet minimize strategy

copy_table = {
    "need_copy": True,
    "batch_num": 100,
    "src_sparse_tables": [1],
    "dest_sparse_tables": [0],
    "src_var_list": ["join_fc_0.w_0"],
    "dest_var_list": ["update_fc_0.w_0"],
}