### What changes were proposed in this pull request?
With benchmark original, where the timestamp values are valid to the new parser
the result is
```scala
[info] Running benchmark: Read dates and timestamps
[info] Running case: timestamp strings
[info] Stopped after 3 iterations, 5781 ms
[info] Running case: parse timestamps from Dataset[String]
[info] Stopped after 3 iterations, 44764 ms
[info] Running case: infer timestamps from Dataset[String]
[info] Stopped after 3 iterations, 93764 ms
[info] Running case: from_json(timestamp)
[info] Stopped after 3 iterations, 59021 ms
```
When we modify the benchmark to
```scala
def timestampStr: Dataset[String] = {
spark.range(0, rowsNum, 1, 1).mapPartitions { iter =>
iter.map(i => s"""{"timestamp":"1970-01-01T01:02:03.${i % 100}"}""")
}.select($"value".as("timestamp")).as[String]
}
readBench.addCase("timestamp strings", numIters) { _ =>
timestampStr.noop()
}
readBench.addCase("parse timestamps from Dataset[String]", numIters) { _ =>
spark.read.schema(tsSchema).json(timestampStr).noop()
}
readBench.addCase("infer timestamps from Dataset[String]", numIters) { _ =>
spark.read.json(timestampStr).noop()
}
```
where the timestamp values are invalid for the new parser which causes a fallback to legacy parser(2.4).
the result is
```scala
[info] Running benchmark: Read dates and timestamps
[info] Running case: timestamp strings
[info] Stopped after 3 iterations, 5623 ms
[info] Running case: parse timestamps from Dataset[String]
[info] Stopped after 3 iterations, 506637 ms
[info] Running case: infer timestamps from Dataset[String]
[info] Stopped after 3 iterations, 509076 ms
```
About 10x perf-regression
BUT if we modify the timestamp pattern to `....HH:mm:ss[.SSS][XXX]` which make all timestamp values valid for the new parser to prohibit fallback, the result is
```scala
[info] Running benchmark: Read dates and timestamps
[info] Running case: timestamp strings
[info] Stopped after 3 iterations, 5623 ms
[info] Running case: parse timestamps from Dataset[String]
[info] Stopped after 3 iterations, 506637 ms
[info] Running case: infer timestamps from Dataset[String]
[info] Stopped after 3 iterations, 509076 ms
```
### Why are the changes needed?
Fix performance regression.
### Does this PR introduce any user-facing change?
NO
### How was this patch tested?
new tests added.
Closes#28181 from yaooqinn/SPARK-31414.
Authored-by: Kent Yao <yaooqinn@hotmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
d65f534c5a