[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.
<?xml version="1.0" encoding="UTF-8"?>
<display window-flags="sticky, below" width="185" height="200">
<sensor id="r" module="rqlsensor"/>
<sensor id="FS" module="FontSelector,1,Sans 10 black"/>
<!-- left border -->
<group x="0" width="5" height="200" bg-uri="gfx/border-left.png"/>
<image x="10" y="0" uri="gfx/logo_erudi.png"/>
<array id="results" x="10" y="30"
watch="layout=r:layout, length=r:length">
<label id="lbls1" color="black"
on-enter="r:enter-line"
on-leave="r:leave-line"
on-click="r:click-line"
watch="value=r:result, font=FS:font0, color=r:resultbg"/>
</array>
</display>