feat(themes): add support for modular themes and custom themes (#30651)

Issue number: internal

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## What is the new behavior?
- Moves `openURL` out of the `theme` utils because it makes more sense
in `helpers`
- Adds support for the default `default.tokens.ts` design tokens file
- Adds support for custom theme set globally and on a component 

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

## Other information

Requires additional changes in order to test.

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

core/src/components/fab-button/fab-button.tsx

@@ -2,9 +2,9 @@ import xRegular from '@phosphor-icons/core/assets/regular/x.svg';
 import type { ComponentInterface, EventEmitter } from '@stencil/core';
 import { Component, Element, Event, Host, Prop, h } from '@stencil/core';
 import type { AnchorInterface, ButtonInterface } from '@utils/element-interface';
-import { inheritAriaAttributes } from '@utils/helpers';
+import { inheritAriaAttributes, openURL } from '@utils/helpers';
 import type { Attributes } from '@utils/helpers';
-import { createColorClasses, hostContext, openURL } from '@utils/theme';
+import { createColorClasses, hostContext } from '@utils/theme';
 import { close } from 'ionicons/icons';
 
 import { config } from '../../global/config';