S3Path implements `getproperty` but not `propertynames`

[ssfrr]

This makes is to the set of properties available with path.X doesn't match the ones you get with propertynames(path).

In particular you don't get key, which is a problem if you're trying to use properties to determine equality between paths:

julia> p1 = S3Path("s3://foo/bar")
p"s3://foo/bar"

julia> p2 = S3Path("s3://foo/baz")
p"s3://foo/baz"

julia> [getproperty(p1, s) for s in propertynames(p1)]
4-element Vector{String}:
 "s3://foo"
 "/"
 "s3://foo/"
 "/"

julia> [getproperty(p2, s) for s in propertynames(p2)]
4-element Vector{String}:
 "s3://foo"
 "/"
 "s3://foo/"
 "/"

julia> propertynames(p1)
(:drive, :root, :anchor, :separator)