Parameterize array in InterlaceOperator

[jishnub]

After this, Dirichlet boundary conditions may be represented using static vectors of concrete Operator types:

julia> Dirichlet(Chebyshev(),2).op.ops
2-element StaticArraysCore.SVector{2, ApproxFunBase.ConcreteEvaluation{Chebyshev{ChebyshevInterval{Float64}, Float64}, ApproxFunBase.Boundary, Int64, Float64}} with indices SOneTo(2):
 ConcreteEvaluation : Chebyshev() → ConstantSpace(Point(-1.0))
 ConcreteEvaluation : Chebyshev() → ConstantSpace(Point(1.0))

[codecov[bot]]

Codecov Report

Patch coverage: 50.00% and project coverage change: -0.03% :warning:

Comparison is base (c31337a) 27.53% compared to head (eb6c5f8) 27.51%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #559 +/- ## ========================================== - Coverage 27.53% 27.51% -0.03% ========================================== Files 80 80 Lines 8379 8382 +3 ========================================== - Hits 2307 2306 -1 - Misses 6072 6076 +4 ``` | [Files Changed](https://app.codecov.io/gh/JuliaApproximation/ApproxFunBase.jl/pull/559?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation) | Coverage Δ | | |---|---|---| | [src/Operators/general/InterlaceOperator.jl](https://app.codecov.io/gh/JuliaApproximation/ApproxFunBase.jl/pull/559?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL09wZXJhdG9ycy9nZW5lcmFsL0ludGVybGFjZU9wZXJhdG9yLmps) | `23.56% <50.00%> (+0.09%)` | :arrow_up: | ... and [2 files with indirect coverage changes](https://app.codecov.io/gh/JuliaApproximation/ApproxFunBase.jl/pull/559/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation)

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