fix(checkbox, toggle): uniform helper text style for ionic theme (#30893)

Issue number: resolves #

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## What is the current behavior?
Helper and Error text style it's not uniform between elements.

## What is the new behavior?
* Changed the typography for `.checkbox-bottom` and `.toggle-bottom` to
use `globals.$ion-body-sm-medium` for a more consistent appearance with
other components.
[[1]](diffhunk://#diff-796ffc72b6171910c25d5aad085bc245095c38f104d55e253e06282702205066L116-R116)
[[2]](diffhunk://#diff-ad6128c5d08f42a970eab3a8c7081eaad590bd4ebbcd19ec4e6110a6f7977040L59-R70)
* Updated the color of `.input-bottom .helper-text` and `.input-bottom
.counter` to use `globals.$ion-text-subtlest` instead of
`globals.$ion-primitives-neutral-800`, and `.input-bottom .error-text`
to use `globals.$ion-text-danger`.
* Standardized `.textarea-bottom .error-text` to use
`globals.$ion-text-danger` and reordered the CSS for clarity, while
`.textarea-bottom .helper-text` and `.textarea-bottom .counter` use
`globals.$ion-text-subtlest`.
* Updated `.toggle-bottom .error-text` to use `globals.$ion-text-danger`
and `.toggle-bottom .helper-text` to use `globals.$ion-text-subtlest`
for improved semantic clarity and consistency.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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