feat(themes): add base tokens and update colors to use new token system (#30692)

## What is the current behavior?
The colors are generated using the Sass functions and a `$colors` map
and the design tokens are undefined.

## What is the new behavior?
- Moves the helper & theme `spec` tests into the `test` directory with
the other ones
- Defines base tokens for the default, light & dark tokens
- Defines the interfaces for the different theme objects
- Adds new theme utility functions to mix colors together (used for
shade & tint) and convert hex to rgb
- Updates the functions that generate the design token variables to:
- Automatically generate the rgb variables without needing to set them
manually
- Create the color classes (`.ion-color-primary`,
`.ion-color-secondary`, etc.) which are used by the components to change
their color via the `color` property
- Adds 3 e2e tests to verify visually that the design tokens are
generating properly: Basic, Color & Typography
- Removes the old Sass mixins/functions & updates the ones we still need
to pull from the design tokens instead of the `$colors` map

## Does this introduce a breaking change?

- [x] Yes
- [ ] No

This adds `foreground` as a required variant to the colors now.
Currently foreground is only used by clear buttons but it should be used
by all text-only components. This will break for any apps overriding
`--ion-color-primary` without `--ion-color-primary-foreground`. We will
have to look into improving the migration path on this later.

## Other information

- [Themes /
Basic](https://ionic-framework-git-fw-6748-ionic1.vercel.app/src/themes/test/basic)
- [Themes /
Color](https://ionic-framework-git-fw-6748-ionic1.vercel.app/src/themes/test/color)
- [Themes /
Typography](https://ionic-framework-git-fw-6748-ionic1.vercel.app/src/themes/test/typography)

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Co-authored-by: Brandy Smith <6577830+brandyscarney@users.noreply.github.com>
Co-authored-by: ionitron <hi@ionicframework.com>

Author: brandyscarney