[YSQL] Fix tuple to string utility functions

[arpang]

Jira Link: DB-15633

Description

Tuple to string utility functions (YbHeapTupleToString(), YbHeapTupleToStringWithIsOmitted(), YbTupleTableSlotToStringWithIsOmitted()) have multiple issues:

• Code duplication across YbHeapTupleToString() and YbHeapTupleToStringWithIsOmitted()
• YbTupleTableSlotToStringWithIsOmitted() calls YbHeapTupleToStringWithIsOmitted(), but it should be the other way around.
  • Even the implementation is incorrect. YbTupleTableSlotToStringWithIsOmitted() incorrectly asserts that shouldFree should be false. This is not the case for virtual and minimal tuple table slots.
  • ExecFetchSlotHeapTuple() expects the slot to be non-empty. YbTupleTableSlotToStringWithIsOmitted() doesn't make any such check before calling it.

Rework these functions.

Issue Type

kind/bug

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