JsonArray optimizations

[magicprinc]

1. remove two wrapper methods fromJson and fromBuffer
2. better .stream() with flags and less lambdas
3. plus 2 ctors: JsonArray(Collection collection) and (initialCapacity)
4. micro optimization with len (it had shown difference in latin1 String→byte[] benchmark)

There was https://github.com/eclipse-vertx/vert.x/pull/4995, but it had no information value