[SPARK-3954][Streaming] Optimization to FileInputDStream

about convert files to RDDS there are 3 loops with files sequence in spark source.
loops files sequence:
1.files.map(...)
2.files.zip(fileRDDs)
3.files-size.foreach
It's will very time consuming when lots of files.So I do the following correction:
3 loops with files sequence => only one loop

Author: surq <surq@asiainfo.com>

Closes #2811 from surq/SPARK-3954 and squashes the following commits:

321bbe8 [surq]  updated the code style.The style from [for...yield]to [files.map(file=>{})]
88a2c20 [surq] Merge branch 'master' of https://github.com/apache/spark into SPARK-3954
178066f [surq] modify code's style. [Exceeds 100 columns]
626ef97 [surq] remove redundant import(ArrayBuffer)
739341f [surq] promote the speed of convert files to RDDS