## What changes were proposed in this pull request?
Improves the explain output of several physical plans by displaying embedded logical plan in tree style
Some physical plan contains a embedded logical plan, for example, `cache tableName query` maps to:
```
case class CacheTableCommand(
tableName: String,
plan: Option[LogicalPlan],
isLazy: Boolean)
extends RunnableCommand
```
It is easier to read the explain output if we can display the `plan` in tree style.
**Before change:**
Everything is messed in one line.
```
scala> Seq((1,2)).toDF().createOrReplaceTempView("testView")
scala> spark.sql("cache table testView2 select * from testView").explain()
== Physical Plan ==
ExecutedCommand CacheTableCommand testView2, Some('Project [*]
+- 'UnresolvedRelation `testView`, None
), false
```
**After change:**
```
scala> spark.sql("cache table testView2 select * from testView").explain()
== Physical Plan ==
ExecutedCommand
: +- CacheTableCommand testView2, false
: : +- 'Project [*]
: : +- 'UnresolvedRelation `testView`, None
```
## How was this patch tested?
Manual test.
Author: Sean Zhong <seanzhong@databricks.com>
Closes#13433 from clockfly/verbose_breakdown_3_2.
c8fb776d4a