add back unsafe_convert to pointer for arrays (#53589)

This caused a pretty big breakage in the ecosystem (~50 packages) and is
according to Jameson "Too breaking for no necessary reason". So let's
add it back.

---------

Co-authored-by: Jameson Nash <vtjnash@gmail.com>
(cherry picked from commit d3ee213)

base/pointer.jl

@@ -64,6 +64,7 @@ unsafe_convert(::Type{Ptr{Int8}}, s::String) = ccall(:jl_string_ptr, Ptr{Int8},
 
 cconvert(::Type{<:Ptr}, a::Array) = getfield(a, :ref)
 unsafe_convert(::Type{Ptr{S}}, a::AbstractArray{T}) where {S,T} = convert(Ptr{S}, unsafe_convert(Ptr{T}, a))
+unsafe_convert(::Type{Ptr{T}}, a::Array{T}) where {T} = unsafe_convert(Ptr{T}, a.ref)
 unsafe_convert(::Type{Ptr{T}}, a::AbstractArray{T}) where {T} = error("conversion to pointer not defined for $(typeof(a))")
 # TODO: add this deprecation to give a better error:
 # cconvert(::Type{<:Ptr}, a::AbstractArray) = error("conversion to pointer not defined for $(typeof(a))")

test/core.jl

@@ -8127,3 +8127,5 @@ let M = @__MODULE__
     @test Core.set_binding_type!(M, :a_typed_global) === nothing
     @test Core.get_binding_type(M, :a_typed_global) === Tuple{Union{Integer,Nothing}}
 end
+
+@test Base.unsafe_convert(Ptr{Int}, [1]) !== C_NULL