[Enhancement] Allow "default" Preload script / Only compile once

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### Problem Description

Right now, every preload script is being compiled separately, taking considerable time to finish. I have quite a lot of renderers, but only a single, central preload script. It would be great if we could decrease the time necessary to compile by compiling the preload script only once.

### Proposed Solution

Cache the paths of preload scripts and, if a path already compiled is encountered, simply copy the compiled version to the new target.

### Alternatives Considered

Another possible solution would be to define a "global" preload in a variable, e.g., named `preloadForAllRenderers` that can be set instead of all the default ones. Depending on how easy it is to access the config, this might be easier to implement, and I can guess that there are a few apps out there that only have a single preload script for all renderers.

### Additional Information

While it is absolutely great to have the ability to set separate preload files, I think most apps only need a single preload file for all windows to keep maintainability and the codebase smaller. By allowing either caching or a single global one would increase compile speed for those apps who only need one.

I guess, looking at the code it might be easier to use a default variable which is being used (if set) for all renderers where no specific preload has been defined.