This prepares PostgreSQL for compatibility with Neon's storage.
Significant changes compared to the PostgreSQL 15 patchset include:

- Backported changes for users and roles are no longer required
- Use RM_NEON_ID for changes in WAL, instead of modifying core WAL records

Co-authored-by: Konstantin Knizhnik <[email protected]>

* Neon logical replication support for PG16

* Log heap rewrite file after creation.

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Co-authored-by: Konstantin Knizhnik <[email protected]>
Co-authored-by: Arseny Sher <[email protected]>

Co-authored-by: Konstantin Knizhnik <[email protected]>

* Update WAL buffers when restoring WAL at compute needed for LR

* Fix copying data in WAL buffers

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Co-authored-by: Konstantin Knizhnik <[email protected]>

PG16 adds new function to SMGR: zeroextend
It's implementation in Neon actually wal-log zero pages of extended relation.
This zero page is wal-logged using XLOG_FPI.
As far as page is zero, the hole optimization (excluding from the image everything between pg_upper and pd_lower) doesn't work.

This PR allows to set hole size to BLCKSZ in case of zero page (PageIsNull() returns true).
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Co-authored-by: Konstantin Knizhnik <[email protected]>

* Prevent output callbacks from hearing about neon-file messages

* Load SLRU segments on demand

refer #8763

* Fix errors in downloading SLRU segments

* Fix build problems

* Undo occcasional changes

* Remove unintenmded changes

* Fix smgr_read_slru_segment

* Determine SLRU kind in extension

* Use ctl->PagePrecedes for SLRU page comparison in SimpleLruDownloadSegment to address wraparround

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Co-authored-by: Konstantin Knizhnik <[email protected]>