[migractions] Better handle removal of RQLConstraint in sync_schema In rdef synchronisation, filter unmodified constraints before processing the sets of old and new constraints. Add a new `constraint_by_eid` method on RelationDefinitionSchema, which eliminates the ambiguity of `constraint_by_type` usage when several constraints of the same type are involved in the same migration. Closes #3633644.

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−# -*- coding: utf-8 -*-
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−# copyright %(year)s %(author)s, all rights reserved.
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−# contact %(author-web-site)s -- mailto:%(author-email)s
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−#
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−%(long-license)s
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−"""%(distname)s views/forms/actions/components for web ui"""