feat: Make asset loading asynchronous and introduce hooks

[hannojg]

No description provided.

[hannojg]

@mrousavy I am getting a crash on android:

2024-03-11 20:37:32.910  3129-3245  libc++abi               com.margelo.filamentexample          E  terminating with uncaught exception of type std::runtime_error: Unable to retrieve jni environment. Is the thread attached?
2024-03-11 20:37:32.910  3129-3247  libc++abi               com.margelo.filamentexample          E  terminating with uncaught exception of type std::runtime_error: Unable to retrieve jni environment. Is the thread attached?
2024-03-11 20:37:32.911  3129-3245  libc                    com.margelo.filamentexample          A  Fatal signal 6 (SIGABRT), code -1 (SI_QUEUE) in tid 3245 (mqt_js), pid 3129 (filamentexample)

[hannojg]

iOS works though

[mrousavy]

fixed