fix(tokens): fix usage on components and review scss architecture (#30368)

Issue number: internal

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## What is the new behavior?
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this PR. -->

Added improvements on scss architecture, as identified on past
assessment, on multiple components.

Some of these changes resulted in snapshots differences, all reviewed
and expected:

- Button spinner - pics with no visual differences/false-positive.
- Item slider -  difference due to updated typography token.
- Item - difference as is now using correct disabled styles tokens.
- searchbar: 1px difference on horizontal margin - expected - to start
using a more rounded value from a token.
- Tab/tab-button - difference as is now using correct typography token.
- Spinner/loading - this looks like a false positive, saw no visible
differences.
- Textarea - this looks like a false positive, saw no visible
differences.
- Typography - this looks like a false positive, saw no visible
differences.

## Does this introduce a breaking change?

- [x] Yes
- [ ] No

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

core/src/components/backdrop/backdrop.ionic.scss

@@ -1,6 +1,8 @@
 @use "../../themes/ionic/ionic.globals.scss" as globals;
-@import "./backdrop";
+@use "./backdrop.common";
 
 :host {
   background-color: rgba(globals.$ion-primitives-base-black-rgb, 0.7);
+
+  z-index: 2;
 }