Fix UserDefaults.float(forKey:) behavior

[woxtu]

This PR fixes UserDefaults.float(forKey:) behavior for missing number values.
https://developer.apple.com/documentation/foundation/userdefaults/1414027-float

UserDefaults.standard.set(true, forKey: "key1")
UserDefaults.standard.set(42, forKey: "key2")
UserDefaults.standard.set(12.34 as Float, forKey: "key3")
UserDefaults.standard.set(12.34, forKey: "key4")
UserDefaults.standard.set("1234", forKey: "key5")

// on macOS
UserDefaults.standard.float(forKey: "key1") // 1
UserDefaults.standard.float(forKey: "key2") // 42
UserDefaults.standard.float(forKey: "key3") // 12.34
UserDefaults.standard.float(forKey: "key4") // 12.34
UserDefaults.standard.float(forKey: "key5") // 1234

// on Linux
UserDefaults.standard.float(forKey: "key1") // 0
UserDefaults.standard.float(forKey: "key2") // 0
UserDefaults.standard.float(forKey: "key3") // 12.34
UserDefaults.standard.float(forKey: "key4") // 0
UserDefaults.standard.float(forKey: "key5") // 1234

[compnerd]

@swift-ci please test

[woxtu]

Thanks!