[Backport][FLINK-38916][FLINK-38417][FLINK-38445][FLINK-39015][table] Backport MultiJoin fixes to 2.1

[gustavodemorais]

• FLINK-38916 - cherry-pick with XML conflict (regenerated)
• FLINK-38417 - added as dependency. Test conflict in MultiJoinSemanticTests.java resolved by keeping existing test programs from 2.1 (e.g. MIXED_CHANGELOG_MODES) and adding the new ones from the cherry-pick (e.g. MULTI_KEY_TYPES)
• FLINK-38445 - added as dependency (XML conflict, regenerated)
• FLINK-39015 - clean cherry-pick after dependencies added
• Fixed: isHeapBackend() adapted for 2.1 API (instanceof HeapKeyedStateBackend instead of getBackendTypeIdentifier()), removed duplicate test methods, replaced addMode() with addOption("changelog-mode", ...)

Minor conflicts mostly related to tests and one naming change.

[flinkbot]

CI report:

• a67c989 Azure: SUCCESS

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[snuyanzin]

thanks for backporting @gustavodemorais

for the future: can you please put links to actual commits in master rather than jira
it is much easier to check it then

[gustavodemorais]

Hey @snuyanzin, sure. Thanks for the note, I'll try to keep that in mind.