swap rweb-cssom to @acemir/cssom for better css nesting support

[acemir]

The updated dependency package enhances the parser's ability to correctly process complex CSS structures, including nested selectors, nested declarations, layer statements and at-rules validations.

Key Changes

Introducing CSS Nesting Module support

• Added support for CSSNestedDeclarations
• CSSStyleRule now inherits properties from CSSGroupingRule

Improved At-Rule Validation

• Refactored at-rule validation logic ensuring that invalid or malformed at-rules are ignored more reliably.
• Improved handling of edge cases, such as unbalanced braces and complex at-rule conditions.
• Enhanced handling of at-rules that cannot be nested.

Improvements in CSS Cascading

• Added support for CSSLayerStatement
• Improves CSSLayerBlockRule interface and layer name validation
• Added support for layerName and supportsText to CSSImportRule

[acemir]

Closes #3885

[domenic]

Exciting! Please add a comment when you get the test suite passing, including making sure there is web platform test coverage for all the new functionality.

[acemir]

Current tests are passing. Now we could look for some coverage increase.