Missing specific subclass type definitions in StylePropertyMapReadOnly.get() return type

[ophirbucai]

Currently, StylePropertyMapReadOnly.get() returns undefined | CSSStyleValue for all CSS properties. This doesn't reflect the CSS Typed OM specification where different properties return specific subclasses like CSSUnitValue, CSSKeywordValue, and CSSTransformValue.

I have a PR ready that addresses this by narrowing down the return types based on property names.