[Strings] string.new_wtf16_array should trap if the end index is less than the start

[kripken]

That is, this should trap, but we did not:

(string.new_wtf16_array
  (array.new_default $array16
    (i32.const 1)
  )
  (i32.const 1)
  (i32.const 0) ;; end is less than the start
)

[tlively]

Hmm, probably worth auditing against the reference implementations given in https://github.com/WebAssembly/js-string-builtins/blob/main/proposals/js-string-builtins/Overview.md to see if we can find any other discrepancies.