typeintersect: fix triangular vars handling outside constructor.

[N5N3]

Fix #57852.
The 'e->triangle' branch doesn't make sense for variables outside the constructor.
Let pkgeval tell us if constraintkind based branches are suitable for handling them.
(The second commit is needed to fix some stack overflow regression.)

[N5N3]

@nanosoldier runtests()

[nanosoldier]

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[N5N3]

@nanosoldier runtests(["MLJTSVDInterface", "CharacteristicInvFourier", "ParameterizedQuantumControl", "AstroForceModels", "SDDP", "DECAES", "PsychomotorVigilanceTask", "ReducedBasis", "DifferentiableBackwardEuler", "VLBIPlots", "ReactionDiffusion", "EarthSciData", "StratIntervals", "BloqadeGates"])

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3 packages failed on the previous version too.

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