[Tab] Add support for tone

[infernova]

📖 Description

• Adds to sgds-tab the following tone variants: neutral, inverse, fixed-light, and fixed-dark.
• Expanded color library with the following colors: --sgds-bg-translucent-inverse-emphasis, --sgds-bg-translucent-fixed-light-emphasis, and --sgds-bg-translucent-fixed-dark-emphasis. All -emphasis variants are 50% opacity variants of exisiting --sgds-bg-translucent-* colors.
• Updated sgds-spinner stories to be easier to read.

Implements #697

✏️ Type of change

• New feature (non-breaking change which adds functionality)

🧪 How Has This Been Tested?

• Updated existing unit test to include tone updates

✅ Checklist:

• My code follows the SGDS style guidelines and naming conventions
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• Any dependent changes have been merged and published in downstream modules

[clukhei]

Pending design from @anzteng