Handle restrictions on MeshSequence

[ksagiyam]

Depend on #382 (small).

In multi-domain (submesh) problems, there are situations where, say, an exterior-facet integration of domainA is an interior-facet integration of domainB. In this PR we extend the Measure class to correctly represent such integration. Specifically, in the above example, if we choose domainA as the "primal" integration domain, we define the interested measure as:

meas = Measure(
    "ds", domainA,
    intersect_measures=(
        Measure("dS", domainB),
    )
)

. This required changing:

• integral sorting (form.py),
• IntegralData grouping (algorithms/domain_analysis.py),
• signature (algorithms/signature.py),

accordingly.

We also modified RestrictionPropagator class and apply_restrictions() function. apply_restriction() function now takes default_restrictions kwarg, so that we can specify the default restrictions domain-wise. In the above case, we will have something like:

apply_restrictions(
    integral,
    default_restrictions={
        domainA: None,
        domainB: "+",
    }
)

.

[mscroggs]

Should this PR be closed in favour of #303? Or this a different feature?

[ksagiyam]

@jorgensd Could we possibly aim to merge this PR this week? I have following PRs, but it would be great to have this merged at least before coming Firedrake workshop.

[jorgensd]

@jorgensd Could we possibly aim to merge this PR this week? I have following PRs, but it would be great to have this merged at least before coming Firedrake workshop.

I'd like some of the other developers to also have a look at this (at the change is rather big, and cascades into different corners of UFL).
@mscroggs @jhale @michalhabera

[ksagiyam]

@jhale If time allows, could you have a look at this?

[schnellerhase]

Could you test if this is still required? The other cases have been resolved, ref. #428.

[ksagiyam]

Looks no longer necessary. I will remove once #428 is merged. Thanks!

[jhale]

Slack conversation on the necessity or not of a more advanced boolean algebra on measures was satisfactory addressed.