Our old `loop_body` function may return single element when `loop_vars` just contains only 1 element, which can cause bug. The key point of this PR is forcing `loop_body` functions always return tuple.

fix launch ps ut test=develop

* nearest_interp op converter w/ dynamic/static

* fix data_layout include

* add trt nearest unit_test

* add nearest_interp NHWC test

* update trt nearest interp nhwc testcase

* remove asterisk for python2 compatibility

* add empty line to prevent conflict

* nearest_interp op converter w/ dynamic/static

* fix data_layout include

* add trt nearest unit_test

* add nearest_interp NHWC test

* update trt nearest interp nhwc testcase

* remove asterisk for python2 compatibility

* add empty line to prevent conflict

* change the priority of out_h, out_w

* add 1f1b scheduler for pp, test=develop

* trt gather converter

* add trt gather unit_test

* fix one ps gradient clip

* add dict/str/list supprot for DataLoader. test=develop

* add serialize unittest

* fix element_op trt plugin serialize bug

* Fix bug with static_convert_var_shape

* replace dot with dash

* add softmax_switch for softmax_with_cross_entropy_op, test=develop

* delete using EigenMatrix in softmax_with_cross_entropy_op.h, test=develop

* add REGISTER_OP_VERSION for softmax_switch attr of softmax_with_cross_entropy_op, test=develop

* fix bug with jit.save

* refine code

* remove the send/recv of tensor size, but users have to specify the shape of the received var explicitly.

* bugfix for test_cholesky_op

* bugfix for test_compare_op

* bugfix for lookup_table_op

* bugfix for affine_channel_op

[Kunlun]Multi xpu dygraph performance optimization , add distributed.spawn support for multi xpu and some bug-fixes (#31130)

* improve performance of depthwise_conv2d

* add unittest

Fix Read-Only Attribute as while_loop Output:

Usually, our convert_while_loop will be like:
```
    [a, b, c] = paddle.jit.dy2static.convert_while_loop(
            condition_name, body_name, [a, b, c])
```
where a, b, c are in loop_var_names.

However, if loop_var_names contains property such as foo.x, we cannot
assign the attribute as output of convert_while_loop because Python
property is a kind of read-only attribute. To handle the case, we replace
the attributes which are output of convert_while_loop with generated
variables, then if we know the attribute is not read-only at runtime, we
assign the attribute. The created statements are like:
```
    [a, b, __attribute_variable_1] = paddle.jit.dy2static.convert_while_loop(
            condition_name, body_name, [a, b, foo.x])
    if not isinstance(getattr(type(foo), x, None), property): foo.x = __attribute_variable_1
```