### What changes were proposed in this pull request?
The PR addresses the issue of compatibility with Spark 2.4 and earlier version in reading/writing dates and timestamp via **Avro** datasource. Previous releases are based on a hybrid calendar - Julian + Gregorian. Since Spark 3.0, Proleptic Gregorian calendar is used by default, see SPARK-26651. In particular, the issue pops up for dates/timestamps before 1582-10-15 when the hybrid calendar switches from/to Gregorian to/from Julian calendar. The same local date in different calendar is converted to different number of days since the epoch 1970-01-01. For example, the 1001-01-01 date is converted to:
- -719164 in Julian calendar. Spark 2.4 saves the number as a value of DATE type into **Avro** files.
- -719162 in Proleptic Gregorian calendar. Spark 3.0 saves the number as a date value.
The PR proposes rebasing from/to Proleptic Gregorian calendar to the hybrid one under the SQL config:
```
spark.sql.legacy.avro.rebaseDateTime.enabled
```
which is set to `false` by default which means the rebasing is not performed by default.
The details of the implementation:
1. Re-use 2 methods of `DateTimeUtils` added by the PR https://github.com/apache/spark/pull/27915 for rebasing microseconds.
2. Re-use 2 methods of `DateTimeUtils` added by the PR https://github.com/apache/spark/pull/27915 for rebasing days.
3. Use `rebaseGregorianToJulianMicros()` and `rebaseGregorianToJulianDays()` while saving timestamps/dates to **Avro** files if the SQL config is on.
4. Use `rebaseJulianToGregorianMicros()` and `rebaseJulianToGregorianDays()` while loading timestamps/dates from **Avro** files if the SQL config is on.
5. The SQL config `spark.sql.legacy.avro.rebaseDateTime.enabled` controls conversions from/to dates, and timestamps of the `timestamp-millis`, `timestamp-micros` logical types.
### Why are the changes needed?
For the backward compatibility with Spark 2.4 and earlier versions. The changes allow users to read dates/timestamps saved by previous version, and get the same result. Also after the changes, users can enable the rebasing in write, and save dates/timestamps that can be loaded correctly by Spark 2.4 and earlier versions.
### Does this PR introduce any user-facing change?
Yes, the timestamp `1001-01-01 01:02:03.123456` saved by Spark 2.4.5 as `timestamp-micros` is interpreted by Spark 3.0.0-preview2 differently:
```scala
scala> spark.conf.set("spark.sql.session.timeZone", "America/Los_Angeles")
scala> spark.read.format("avro").load("/Users/maxim/tmp/before_1582/2_4_5_date_avro").show(false)
+----------+
|date |
+----------+
|1001-01-07|
+----------+
```
After the changes:
```scala
scala> spark.conf.set("spark.sql.legacy.avro.rebaseDateTime.enabled", true)
scala> spark.conf.set("spark.sql.session.timeZone", "America/Los_Angeles")
scala> spark.read.format("avro").load("/Users/maxim/tmp/before_1582/2_4_5_date_avro").show(false)
+----------+
|date |
+----------+
|1001-01-01|
+----------+
```
### How was this patch tested?
1. Added tests to `AvroLogicalTypeSuite` to check rebasing in read. The test reads back avro files saved by Spark 2.4.5 via:
```shell
$ export TZ="America/Los_Angeles"
```
```scala
scala> spark.conf.set("spark.sql.session.timeZone", "America/Los_Angeles")
scala> val df = Seq("1001-01-01").toDF("dateS").select($"dateS".cast("date").as("date"))
df: org.apache.spark.sql.DataFrame = [date: date]
scala> df.write.format("avro").save("/Users/maxim/tmp/before_1582/2_4_5_date_avro")
scala> val df2 = Seq("1001-01-01 01:02:03.123456").toDF("tsS").select($"tsS".cast("timestamp").as("ts"))
df2: org.apache.spark.sql.DataFrame = [ts: timestamp]
scala> df2.write.format("avro").save("/Users/maxim/tmp/before_1582/2_4_5_ts_avro")
scala> :paste
// Entering paste mode (ctrl-D to finish)
val timestampSchema = s"""
| {
| "namespace": "logical",
| "type": "record",
| "name": "test",
| "fields": [
| {"name": "ts", "type": ["null", {"type": "long","logicalType": "timestamp-millis"}], "default": null}
| ]
| }
|""".stripMargin
// Exiting paste mode, now interpreting.
scala> df3.write.format("avro").option("avroSchema", timestampSchema).save("/Users/maxim/tmp/before_1582/2_4_5_ts_millis_avro")
```
2. Added the following tests to `AvroLogicalTypeSuite` to check rebasing of dates/timestamps (in microsecond and millisecond precision). The tests write rebased a date/timestamps and read them back w/ enabled/disabled rebasing, and compare results. :
- `rebasing microseconds timestamps in write`
- `rebasing milliseconds timestamps in write`
- `rebasing dates in write`
Closes#27953 from MaxGekk/rebase-avro-datetime.
Authored-by: Maxim Gekk <max.gekk@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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