Add an internal _value_from_datadict() method to BaseForm

[Chris Jerdonek]

I noticed that some call sites can be simplified if an internal method called something like _value_from_datadict() is added to BaseForm. Here is one of the call sites: ​https://github.com/django/django/blob/6f60fa97b0b501ef7cc77e16392654bf27ec8db3/django/forms/boundfield.py#L121

Its implementation can look something like this:

def _value_from_datadict(self, field, html_name):
    return field.widget.value_from_datadict(self.data, self.files, html_name)

One reason this is nicer is that callers don't have to know about the form's self.data and self.files dicts. They can just access a method on the form, which encapsulates the data dictionaries.

[Chris Jerdonek]

PR: ​https://github.com/django/django/pull/14629

[GitHub <noreply@…>]

In 4be58fc:

Fixed #32917 -- Added BaseForm._widget_data_value()/_field_data_value().