fix(many): update form controls (radio, checkbox, toggle, input, select) to have consistent disabled opacity (#27396)

Issue number: resolves #27184

---------

## What is the current behavior?
The modern form controls do not use the same opacity for their labels
when disabled, resulting in inconsistent UI when using two different
types in the same view (select vs checkbox, for example).

## What is the new behavior?
The checkbox, input, radio, range, select, textarea and toggle labels
have been updated on both modes to use the same opacity as each other
when disabled. The checkbox and radio icons have been updated to use a
different opacity than the label for `md` mode.

- Updates `ios` mode so all form controls use the same opacity of `0.3`
- I could not find any guidelines by Apple for what color these should
be, so I decided to just make them the same as what is most commonly
used & match item
- Updates `md` mode so all form control labels use the same opacity of
`0.38`
- I used the [Material Design 3
documentation](https://m2.material.io/components) to get this number as
well as the opacity of the disabled selection controls in the [Material
Design 2 figma design
kit](https://www.figma.com/community/file/778763161265841481). The
Material Design 2 documentation does not mention the opacity, but this
is also the number used by Material Design 1 so it's safe to assume it
is what the disabled form labels should also use for Material Design 2.
- Updates the `md` range so the slotted elements are also included when
setting the opacity on the label
- Updates the range, radio & checkbox tests to make sure there are
screenshots in the different disabled states
- Updates the item/disabled test to include radio & textarea so you can
see all form controls side by side

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

## Other information

I downloaded screenshots of the item disabled tests and put them side by
side for `main` and this branch in order to see the differences in the
labels. The grey boxes to the left of each item are just a bigger
version of the label color for that item, so it's easier to see when
they aren't the same.

![iOS before and
after](https://github.com/ionic-team/ionic-framework/assets/6577830/2ce53625-e4e3-4565-a741-a47e27cf0275)
![MD before and
after](https://github.com/ionic-team/ionic-framework/assets/6577830/9cd83cdc-ab45-49bf-a0dc-1d78ba7f43be)

---------

Co-authored-by: ionitron <hi@ionicframework.com>

core/src/components/checkbox/checkbox.md.vars.scss

@@ -4,8 +4,8 @@
 // Material Design Checkbox
 // --------------------------------------------------
 
-/// @prop - Opacity of the disabled checkbox
-$checkbox-md-disabled-opacity:           .3 !default;
+/// @prop - Opacity of the disabled checkbox label
+$checkbox-md-disabled-opacity:           $form-control-md-disabled-opacity !default;
 
 /// @prop - Background color of the checkbox icon when off
 $checkbox-md-icon-background-color-off:  $item-md-background !default;
@@ -72,3 +72,12 @@ $checkbox-md-item-end-margin-bottom:     $checkbox-md-item-end-margin-top !defau
 
 /// @prop - Margin start of the end checkbox item
 $checkbox-md-item-end-margin-start:      0 !default;
+
+/// @prop - Opacity of the disabled checkbox
+/// This value is used because the checkbox color is set to
+/// `rgb(0, 0, 0, 0.60)` when enabled and we need it to be
+/// `rgb(0, 0, 0, 0.38)` when disabled but the disabled
+/// opacity is applied on top of the transparent color so
+/// this opacity gets us the equivalent of applying `0.38`
+/// on top of an opaque checkbox `rgb(0, 0, 0, 1.0)`
+$checkbox-md-icon-disabled-opacity:      0.63 !default;