[SQL] remove a decimal case branch that has no effect at runtime

it generates warnings at compile time marmbrus

Author: Xiangrui Meng <meng@databricks.com>

Closes #3192 from mengxr/dtc-decimal and squashes the following commits:

955e9fb [Xiangrui Meng] remove a decimal case branch that has no effect

(cherry picked from commit d793d80c8084923ea04dcf7d268eec8ede490127)
Signed-off-by: Michael Armbrust <michael@databricks.com>
[SPARK-4250] [SQL] Fix bug of constant null value mapping to ConstantObjectInspector

Author: Cheng Hao <hao.cheng@intel.com>

Closes #3114 from chenghao-intel/constant_null_oi and squashes the following commits:

e603bda [Cheng Hao] fix the bug of null value for primitive types
50a13ba [Cheng Hao] fix the timezone issue
f54f369 [Cheng Hao] fix bug of constant null value for ObjectInspector

(cherry picked from commit fa777833b52b6f339cdc335e8e3935cfe9a2a7eb)
Signed-off-by: Michael Armbrust <michael@databricks.com>
[SPARK-4149][SQL] ISO 8601 support for json date time strings

This implement the feature davies mentioned in https://github.com/apache/spark/pull/2901#discussion-diff-19313312

Author: Daoyuan Wang <daoyuan.wang@intel.com>

Closes #3012 from adrian-wang/iso8601 and squashes the following commits:

50df6e7 [Daoyuan Wang] json data timestamp ISO8601 support

(cherry picked from commit a1fc059b69c9ed150bf8a284404cc149ddaa27d6)
Signed-off-by: Michael Armbrust <michael@databricks.com>
[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

(cherry picked from commit ce6ed2abd14de26b9ceaa415e9a42fbb1338f5fa)
Signed-off-by: Tathagata Das <tathagata.das1565@gmail.com>