[HTML5] Fix JavaScript string parsing with new interface.
[HTML5] Fix JavaScript string parsing with new interface.

Strings are UTF-8 encoded and should be parsed as such, while it was
being parsed as a C string before.

(cherry picked from commit d4e302a3a499b4a3445b4e1610757fc310d1641d)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot