refactor: simplify `waitForFontsLoaded()`

[MichaHuhn]

Simplify the waitForFontsLoaded() function in the fontStatusStore.

The callback function will be executed whenever the fontsLoaded ref is true. Because it should only be executed once, the once option is set to true. If fontsLoaded is already true, the callback function is executed immediately because the immediate option is set to true. If fontsLoaded is not true yet, the callback function will be executed as soon as fontsLoaded is true.