[colocation] Make reads aware of table-level tombstone

[jaki]

Reads from SELECTs and point UPDATEs on a colocated table should be aware of table-level tombstones denoting the deletion of tables. Timestamps should be taken into account such that rows at a hybrid time earlier than the table-level tombstone are considered deleted. For example, a TRUNCATE TABLE followed by a SELECT on a colocated table should not surface the old values.

This is step 3 of 4 for the data deletion of the drop flow, issue #3035.