### What changes were proposed in this pull request?
Reprocess all PostgreSQL dialect related PRs, listing in order:
- #25158: PostgreSQL integral division support [revert]
- #25170: UT changes for the integral division support [revert]
- #25458: Accept "true", "yes", "1", "false", "no", "0", and unique prefixes as input and trim input for the boolean data type. [revert]
- #25697: Combine below 2 feature tags into "spark.sql.dialect" [revert]
- #26112: Date substraction support [keep the ANSI-compliant part]
- #26444: Rename config "spark.sql.ansi.enabled" to "spark.sql.dialect.spark.ansi.enabled" [revert]
- #26463: Cast to boolean support for PostgreSQL dialect [revert]
- #26584: Make the behavior of Postgre dialect independent of ansi mode config [keep the ANSI-compliant part]
### Why are the changes needed?
As the discussion in http://apache-spark-developers-list.1001551.n3.nabble.com/DISCUSS-PostgreSQL-dialect-td28417.html, we need to remove PostgreSQL dialect form code base for several reasons:
1. The current approach makes the codebase complicated and hard to maintain.
2. Fully migrating PostgreSQL workloads to Spark SQL is not our focus for now.
### Does this PR introduce any user-facing change?
Yes, the config `spark.sql.dialect` will be removed.
### How was this patch tested?
Existing UT.
Closes#26763 from xuanyuanking/SPARK-30125.
Lead-authored-by: Yuanjian Li <xyliyuanjian@gmail.com>
Co-authored-by: Maxim Gekk <max.gekk@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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