feat(styles): add xxl border-radius option

[KareemDa]

Description

add option: 2xl to border radius

Motivation and Context

th step between lg, xl was too big, So I've added new value between

old code:

• 'lg': $border-radius-root * 2
• 'xl': $border-radius-root * 6

new code:

• 'lg': $border-radius-root * 2
• 'xl': $border-radius-root * 4
• '2xl': $border-radius-root * 6

How Has This Been Tested?

Markup:

// Paste your FULL Playground.vue here

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and backwards compatible changes and next for non-backwards compatible changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)