## What changes were proposed in this pull request?
Support Decimal type push down to the parquet data sources.
The Decimal comparator used is: [`BINARY_AS_SIGNED_INTEGER_COMPARATOR`](c6764c4a08/parquet-column/src/main/java/org/apache/parquet/schema/PrimitiveComparator.java (L224-L292)).
## How was this patch tested?
unit tests and manual tests.
**manual tests**:
```scala
spark.range(10000000).selectExpr("id", "cast(id as decimal(9)) as d1", "cast(id as decimal(9, 2)) as d2", "cast(id as decimal(18)) as d3", "cast(id as decimal(18, 4)) as d4", "cast(id as decimal(38)) as d5", "cast(id as decimal(38, 18)) as d6").coalesce(1).write.option("parquet.block.size", 1048576).parquet("/tmp/spark/parquet/decimal")
val df = spark.read.parquet("/tmp/spark/parquet/decimal/")
spark.sql("set spark.sql.parquet.filterPushdown.decimal=true")
// Only read about 1 MB data
df.filter("d2 = 10000").show
// Only read about 1 MB data
df.filter("d4 = 10000").show
spark.sql("set spark.sql.parquet.filterPushdown.decimal=false")
// Read 174.3 MB data
df.filter("d2 = 10000").show
// Read 174.3 MB data
df.filter("d4 = 10000").show
```
Author: Yuming Wang <yumwang@ebay.com>
Closes#21556 from wangyum/SPARK-24549.
9549a28149