Re: XID formatting and SLRU refactorings (was: Add 64-bit XIDs into PostgreSQL 15)

As suggested before by Heikki Linnakangas, I've added a patch for making 2PC transaction state 64-bit.

At first, my intention was to rebuild all twophase interface to use FullTransactionId. But doing this in a proper

manner would lead to switching from TransactionId to FullTransactionId in PGPROC and patch become too

big to handle here.

So I decided to keep it simple for now and use wrap logic trick and calc FullTransactionId on current epoch,

since the span of active xids cannot exceed one epoch at any given time.