Specialize 2-arg show for LinearIndices (JuliaLang#56482)

After this,
```julia
julia> l = LinearIndices((1:3, 1:4));

julia> show(l)
LinearIndices((1:3, 1:4))
```
The printed form is a valid constructor.

Author: jishnub

base/indices.jl

@@ -576,3 +576,7 @@ first(iter::LinearIndices) = 1
 first(iter::LinearIndices{1}) = (@inline; first(axes1(iter.indices[1])))
 last(iter::LinearIndices) = (@inline; length(iter))
 last(iter::LinearIndices{1}) = (@inline; last(axes1(iter.indices[1])))
+
+function show(io::IO, iter::LinearIndices)
+    print(io, "LinearIndices(", iter.indices, ")")
+end

test/abstractarray.jl

@@ -335,6 +335,15 @@ end
         R = LinearIndices((Base.IdentityUnitRange(0:1), 0:1))
         @test axes(R) == (Base.IdentityUnitRange(0:1), Base.OneTo(2))
     end
+
+    @testset "show" begin
+        A = zeros(2,3)
+        for B in (A, view(A, Base.IdentityUnitRange(2:4)))
+            l = LinearIndices(B)
+            s = sprint(show, l)
+            @test s == "LinearIndices($(axes(B)))"
+        end
+    end
 end
 
 @testset "copy for LinearIndices/CartesianIndices" begin