Update tracking for Customizable Select feature

[davidmcguiredesign]

Caniuse currently tracks the <selectlist> element. The feature is designed to solve something that has been a particular point of frustration for web devs for years, and is exactly the kind of feature for which I regularly return to Caniuse. The feature is nearer to completion than ever, but it has been renamed (again).

• Open UI lists this feature as "Customizable Select" and notes that it has been renamed
• Chrome has a prototype in Chrome Canary (130+)
• WHATWG has moved it to Stage 3 on Feb 14, 2025 under the name "Customizable Select"

In addition to selectmenu (the older element) which already returns the feature via search, Chrome's announcement lists several other differentiating keywords: appearance:base-select, ::picker(select), and selectedoption (singular, a new element). Until adoption is official, it might make sense to return the same single entry for all these keywords.