TableAM: New interface to accommodate state for DML operations

[Eulerizeit]

Insert/update/Delete are considered stateless which is true only for HEAP.

Examples of that state could be:
datum streams -- they need to be open for the duration of the operation
??? --

In order to show that in-tree AMs benefit we will show that the next insert will be potentially faster

implementation thought (not have to lock visability map page and could use a pin. )

Unfonf notes:
https://wiki.postgresql.org/wiki/PgCon_2020_Developer_Unconference/tableAM_next_steps
From meeting: "in-tree AMs as well may benefit from state, e.g. pin the last visibility map page."