Issue #3480712 by benstallings: Fix entity browser losing selection on cardinality-1 IEF submits

In getEntitiesByTargetId(), broaden the IEF-submit detection so cardinality-1 fields nested inside an Inline Entity Form are recognized: the entity browser's own submit button (whose #name ends in "_entity_browser_entity_browser", per EntityBrowserElement::#eb_parents and Modal::displayEntityBrowser()) now triggers the same target_id lookup that "ief-edit-submit" does. Also guard against a NULL $current_user_input so it isn't passed to EntityBrowserElement::processEntityIds().

Reworked from patch #6: dropped the isset() wrapper around $is_relevant_submit because it changed fall-through semantics (left it TRUE when the expected #parents key was absent), and replaced the patch's str_contains substring match with a suffix-anchored str_ends_with so the check doesn't depend on the configured browser machine name.

Closes #3480712