DistributedSampler with GeneratorOp bug
Issue#2:
GeneratorOp with iterable source doesn't respect num_samples
Issue#3:
Generator with schemas does not take samplers

From: @tina_mengting_zhang
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From: @peilin-wang
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fix ci

fix ci

fixed test cases and ci

fixed test cases and ci

From: @cathwong
Reviewed-by: @nsyca,@robingrosman
Signed-off-by: @robingrosman

From: @mengyuanli
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From: @mengyuanli
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From: @huaweib
Reviewed-by: @kisnwang,@zhoufeng54
Signed-off-by: @zhoufeng54

From: @yepei6
Reviewed-by: @kisnwang,@kingxian
Signed-off-by: @kingxian

From: @zh_qh
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From: @jinyaohui
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From: @zhouyaqiang0
Reviewed-by: @wuxuejian,@oacjiewen,@wuxuejian
Signed-off-by: @wuxuejian

From: @zhouyaqiang0
Reviewed-by: @wuxuejian,@oacjiewen,@wuxuejian
Signed-off-by: @wuxuejian

From: @HulkTang
Reviewed-by: @kisnwang,@zhoufeng54
Signed-off-by: @zhoufeng54

From: @yuchaojie
Reviewed-by: @kisnwang,@zhoufeng54
Signed-off-by: @zhoufeng54

From: @yuchaojie
Reviewed-by: @kisnwang,@zhoufeng54
Signed-off-by: @zhoufeng54

From: @shuzigood
Reviewed-by: @wuxuejian,@linqingke
Signed-off-by: @wuxuejian

From: @jjfeing
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From: @limingqi107
Reviewed-by: @kisnwang,@cristoval
Signed-off-by: @cristoval

From: @nsyca
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From: @sl_wang
Reviewed-by: @wang_zi_dong
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From: @probiotics_53
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From: @irmo
Reviewed-by: @zhoufeng54,@chujinjin
Signed-off-by: @chujinjin

From: @zyli2020
Reviewed-by: @cristoval,@limingqi107
Signed-off-by: @limingqi107

From: @zhujingxuan
Reviewed-by: @zhanghaibo5,@wangchengyuan
Signed-off-by: @zhanghaibo5

From: @lihongkang1
Reviewed-by: @liangchenghui,@wuxuejian
Signed-off-by: @liangchenghui

From: @liuyang_655
Reviewed-by: @kingxian,@zhunaipan
Signed-off-by: @kingxian

From: @yangruoqi713
Reviewed-by: @zhang_xue_tong,@hangangqiang
Signed-off-by: @zhang_xue_tong

(cherry picked from commit 0c0723272a)

From: @alouhahahahaha
Reviewed-by: @kisnwang
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From: @zoloft
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From: @wangshuide2020
Reviewed-by: @liangchenghui,@wuxuejian
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From: @yangzhenzhang
Reviewed-by: @stsuteng
Signed-off-by: @stsuteng

From: @liangzhibo
Reviewed-by: @ginfung,@zh_qh
Signed-off-by: @zh_qh

From: @laiyongqiang
Reviewed-by: @stsuteng,@zhoufeng54
Signed-off-by: @stsuteng

From: @laiyongqiang
Reviewed-by: @stsuteng,@zhoufeng54
Signed-off-by: @stsuteng

From: @zhangyunshu
Reviewed-by: @yelihua
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From: @ouwenchang
Reviewed-by: @lixiaohui33,@yelihua
Signed-off-by: @yelihua

From: @shibeiji
Reviewed-by: @c_34,@guoqi1024
Signed-off-by: @c_34