Rename helper functions to avoid namespace conflicts

There are some helper/utility functions in this module with generic names like flatten_array_by_cids and _replace_value_in_recursive and _array_flatten that should be renamed to include the name of the module.

Though it's true that these are not hooks and do not *need* the name of the module to work properly, there is a high risk that another module might also define a function named _array_flatten, which could cause us both problems. If we were to name this function _authorizenetwebform_array_flatten instead, all problems could be avoided.