## What changes were proposed in this pull request?
It seems this is a regression assuming from https://issues.apache.org/jira/browse/SPARK-16698.
Field name having dots throws an exception. For example the codes below:
```scala
val path = "/tmp/path"
val json =""" {"a.b":"data"}"""
spark.sparkContext
.parallelize(json :: Nil)
.saveAsTextFile(path)
spark.read.json(path).collect()
```
throws an exception as below:
```
Unable to resolve a.b given [a.b];
org.apache.spark.sql.AnalysisException: Unable to resolve a.b given [a.b];
at org.apache.spark.sql.catalyst.plans.logical.LogicalPlan$$anonfun$resolve$1$$anonfun$apply$5.apply(LogicalPlan.scala:134)
at org.apache.spark.sql.catalyst.plans.logical.LogicalPlan$$anonfun$resolve$1$$anonfun$apply$5.apply(LogicalPlan.scala:134)
at scala.Option.getOrElse(Option.scala:121)
```
This problem was introduced in 17eec0a71b (diff-27c76f96a7b2733ecfd6f46a1716e153R121)
When extracting the data columns, it does not count that it can contains dots in field names. Actually, it seems the fields name are not expected as quoted when defining schema. So, It not have to consider whether this is wrapped with quotes because the actual schema (inferred or user-given schema) would not have the quotes for fields.
For example, this throws an exception. (**Loading JSON from RDD is fine**)
```scala
val json =""" {"a.b":"data"}"""
val rdd = spark.sparkContext.parallelize(json :: Nil)
spark.read.schema(StructType(Seq(StructField("`a.b`", StringType, true))))
.json(rdd).select("`a.b`").printSchema()
```
as below:
```
cannot resolve '```a.b```' given input columns: [`a.b`];
org.apache.spark.sql.AnalysisException: cannot resolve '```a.b```' given input columns: [`a.b`];
at org.apache.spark.sql.catalyst.analysis.package$AnalysisErrorAt.failAnalysis(package.scala:42)
```
## How was this patch tested?
Unit tests in `FileSourceStrategySuite`.
Author: hyukjinkwon <gurwls223@gmail.com>
Closes#14339 from HyukjinKwon/SPARK-16698-regression.
79826f3c79