Arrow Table doesn't implement `==` for value equality

I was surprised by this when I was writing a unit test that a function returned the expected structure.

For example:
```julia
julia> t = let io = IOBuffer(); Arrow.write(io, (v1=collect(1:10),)); seekstart(io); Arrow.Table(io) end
Arrow.Table with 10 rows, 1 columns, and schema:
:v1 Int64

julia> t2 = let io = IOBuffer(); Arrow.write(io, (v1=collect(1:10),)); seekstart(io); Arrow.Table(io) end
Arrow.Table with 10 rows, 1 columns, and schema:
:v1 Int64

julia> t == t2
false
```

Is the reason for this because it would be too expensive? I think users generally understand that `==` on large collections is expensive and should probably be avoided. Or is it because we don't want to have to implement an expensive `hash()` function, and we'd have to do that if we implement `==`?

Thanks! :)

The issue names no implementation files, tests, or entry points. Start by locating Arrow.Table equality and hashing behavior, then determine the intended semantics and add a regression test that defines when two tables should compare equal.

Written by the indexing model from the issue text.