Add `scale` as a unitless property (#25601)

## Summary CSS has a new property called `scale` (`scale: 2` is a shorthand for `transform: scale(2)`). In vanilla JavaScript, we can do the following: ```js document.querySelector('div').scale = 2; ``` which will make the `<div>` twice as big. So in JavaScript, it is possible to pass a plain number. However, in React, the following does not work currently: ```js <div style={{scale: 2}}> ``` because `scale` is not in the list of unitless properties. This PR adds `scale` to the list. ## How did you test this change? I built `react` and `react-dom` from source and copied it into the node_modules of my project and verified that now `<div style={{scale: 2}}>` does indeed work whereas before it did not.