Issue #3614667 by miwayha: Combine hook_entity_field_access() implementations

EntityAccessControlHandler::fieldAccess() collected hook results as separate arrays keyed by module name, then merged them with array_merge(). When a module implemented hook_entity_field_access() more than once, later results overwrote earlier ones under the same key. This dropped access decisions and their cacheable metadata.

This change accumulates each module's results directly and combines repeated implementations with orIf(), matching the handling of other multi-implementation hooks. Adds a kernel test with two hook_entity_field_access() implementations in one module, each targeting a different field, to confirm both results apply.

Closes #3614667