feat(ngList): use ngTrim to manage whitespace handling when splitting

With the removal of regular expression support `ngList` no longer supported
splitting on newlines (and other pure whitespace splitters).

This change allows the application developer to specify whether whitespace
should be respected or trimmed by using the `ngTrim` attribute. This also
makes `ngList` consistent with the standard use of `ngTrim` in input directives
in general.

Related To: #4344