Closes #12246: General cleanup of utilities modules

* Clean up base modules

* Clean up forms modules

* Clean up templatetags modules

* Replace custom simplify_decimal filter with floatformat

* Misc cleanup

* Merge ReturnURLForm into ConfirmationForm

* Clean up import statements for utilities.forms

* Fix field class references in docs

netbox/utilities/forms/widgets/select.py

@@ -0,0 +1,79 @@
+from django import forms
+
+from utilities.choices import ColorChoices
+from ..utils import add_blank_choice
+
+__all__ = (
+    'BulkEditNullBooleanSelect',
+    'ColorSelect',
+    'HTMXSelect',
+    'SelectDurationWidget',
+    'SelectSpeedWidget',
+    'SelectWithPK',
+)
+
+
+class BulkEditNullBooleanSelect(forms.NullBooleanSelect):
+    """
+    A Select widget for NullBooleanFields
+    """
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        # Override the built-in choice labels
+        self.choices = (
+            ('1', '---------'),
+            ('2', 'Yes'),
+            ('3', 'No'),
+        )
+        self.attrs['class'] = 'netbox-static-select'
+
+
+class ColorSelect(forms.Select):
+    """
+    Extends the built-in Select widget to colorize each <option>.
+    """
+    option_template_name = 'widgets/colorselect_option.html'
+
+    def __init__(self, *args, **kwargs):
+        kwargs['choices'] = add_blank_choice(ColorChoices)
+        super().__init__(*args, **kwargs)
+        self.attrs['class'] = 'netbox-color-select'
+
+
+class HTMXSelect(forms.Select):
+    """
+    Selection widget that will re-generate the HTML form upon the selection of a new option.
+    """
+    def __init__(self, hx_url='.', hx_target_id='form_fields', attrs=None, **kwargs):
+        _attrs = {
+            'hx-get': hx_url,
+            'hx-include': f'#{hx_target_id}',
+            'hx-target': f'#{hx_target_id}',
+        }
+        if attrs:
+            _attrs.update(attrs)
+
+        super().__init__(attrs=_attrs, **kwargs)
+
+
+class SelectWithPK(forms.Select):
+    """
+    Include the primary key of each option in the option label (e.g. "Router7 (4721)").
+    """
+    option_template_name = 'widgets/select_option_with_pk.html'
+
+
+class SelectDurationWidget(forms.NumberInput):
+    """
+    Dropdown to select one of several common options for a time duration (in minutes).
+    """
+    template_name = 'widgets/select_duration.html'
+
+
+class SelectSpeedWidget(forms.NumberInput):
+    """
+    Speed field with dropdown selections for convenience.
+    """
+    template_name = 'widgets/select_speed.html'