inference: propagate partially initialized mutable structs more

[aviatesk]

Following up #55297.
A mutable struct can have undefined fields in a non-contiguous manner, but PartialStruct cannot model such a state. So in #55297 PartialStruct was used to represent only the mutable objects where the field following the minimum initialized fields is also defined.

As a follow-up for the PR, this commit implements a minor improvement that, in cases when the mutable object is already represented as a PartialStruct, allows inference to add one more isdefined-field information on top of those implied by its fields.

mutable struct PartiallyInitialized2
    a; b; c
    PartiallyInitialized2(a) = (@nospecialize; new(a))
    PartiallyInitialized2(a, b) = (@nospecialize; new(a, b))
    PartiallyInitialized2(a, b, c) = (@nospecialize; new(a, b, c))
end

@test Base.infer_effects((PartiallyInitialized2,); optimize=false) do x
    if isdefined(x, :b)
        if isdefined(x, :c)
            return x.c
        end
        return x.b
    end
    return nothing
end |> Core.Compiler.is_nothrow

@nanosoldier runtests()

[nanosoldier]

The package evaluation job you requested has completed - possible new issues were detected.
The full report is available.

[aviatesk]

@nanosoldier runtests(["ASEconvert", "EarlyStopping", "BayesianQuadrature", "HMMER", "LazySets", "GeometricIntegrators", "AstrodynamicalModels", "TimeseriesFeatures", "DifferentialEvolutionMCMC", "ClimaDiagnostics", "SpeedyWeather", "CellMLToolkit", "FaultTolerantControl", "CellularPotts", "HighVoronoi", "VLBIPlots", "EnvironmentalTransport", "QuantumAnnealingAnalytics"])

[nanosoldier]

The package evaluation job you requested has completed - no new issues were detected.
The full report is available.