Potential behavioral change for ANSI MERGE statement with DELETE action

See MB-60762.

For an ANSI MERGE statement with only DELETE option specified, our previous behavior (7.2.x and earlier) is not compliant with SQL standard. Specifically, if a target document (to be deleted) matches with multiple source documents, the SQL standard specifies that an error should be returned, but in 7.2.x we may not return an error depending on how fast the target document is deleted vs a duplicate join result (between the relevant target document and multiple source document) being generated.

The fix for MB-60762 (in 7.6.0 and later) ensures that we now returns an error in such situations. This is for compliance with SQL standard, and should be noted in release note.