use copy_all_files_in_dir to replace copy_files

[daquexian]

将拷贝文件的逻辑从 “在 cmake 阶段获取文件夹里的所有文件，在 make 阶段拷贝文件” 改为 “在 make 阶段拷贝文件夹里的所有文件”

[github-actions]

Speed stats:

GPU Name: GeForce GTX 1080 

PyTorch resnet50 time: 141.7ms (= 7084.8ms / 50, input_shape=[16, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 128.9ms (= 6445.1ms / 50, input_shape=[16, 3, 224, 224], backward is enabled)
Relative speed: 1.10 (= 141.7ms / 128.9ms)

PyTorch resnet50 time: 85.2ms (= 4261.8ms / 50, input_shape=[8, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 74.6ms (= 3730.4ms / 50, input_shape=[8, 3, 224, 224], backward is enabled)
Relative speed: 1.14 (= 85.2ms / 74.6ms)

PyTorch resnet50 time: 56.9ms (= 2843.9ms / 50, input_shape=[4, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 50.9ms (= 2544.1ms / 50, input_shape=[4, 3, 224, 224], backward is enabled)
Relative speed: 1.12 (= 56.9ms / 50.9ms)

PyTorch resnet50 time: 44.5ms (= 2227.1ms / 50, input_shape=[2, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 41.7ms (= 2085.8ms / 50, input_shape=[2, 3, 224, 224], backward is enabled)
Relative speed: 1.07 (= 44.5ms / 41.7ms)

PyTorch resnet50 time: 39.8ms (= 1987.6ms / 50, input_shape=[1, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 38.5ms (= 1925.3ms / 50, input_shape=[1, 3, 224, 224], backward is enabled)
Relative speed: 1.03 (= 39.8ms / 38.5ms)