[SPARK-30869][SQL] Convert dates to/from timestamps in microseconds precision

[younggyuchun]

What changes were proposed in this pull request?

This PR aims to replace functions in DateTimeUtils that convert dates to/from "timestamp" in millisecond precision.

1. Replace millisToDays by microsToDays in DateTimeUtils.
2. Replace daysToMillis by daysToMicros in DateTimeUtils.

Why are the changes needed?

Spark should reduce overhead costs to convert dates to a timestamp in milliseconds as TimestamType values in the Catalyst are stored as microseconds. Recently we switched to Java 8 time API so we do not need to convert to milliseconds.

Does this PR introduce any user-facing change?

No

How was this patch tested?

Pass the Jenkins with the existing tests.

[younggyuchun]

I can't add MaxGekk as a reviewer. cc @MaxGekk

[SparkQA]

Test build #118741 has finished for PR 27661 at commit 0fd79de.

• This patch fails to build.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #118744 has finished for PR 27661 at commit 130baec.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[MaxGekk]

This PR is a duplicate work of my PR #27618 opened 3 days ago. I would like to kindly ask you to close it. /cc @cloud-fan @dongjoon-hyun @srowen @HyukjinKwon

[HyukjinKwon]

Let's close and review #27618