findCanvasEventTarget doesn't use specialHTMLTargets

Please include the following in your bug report:

**Version of emscripten/emsdk:**
```
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.71 (4171ae200b77a6c266b0e1ebb507d61d1ade3501)
clang version 20.0.0git (https:/github.com/llvm/llvm-project d6344c1cd0d099f8d99ee320f33fc9254dbe8288)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /home/jcoa2018/.local/src/emsdk/upstream/bin
```

This line in `library_html5.js`:

https://github.com/emscripten-core/emscripten/blob/f0cc3d004bcbc29a4a5421d54e884d4c42b05218/src/library_html5.js#L366

Seems like it should fall back to findEventTarget, not manual document querying/ID lookup. At a minimum, it should check `specialHTMLTargets[target]` as well as the other options.

Right now, if you follow the docs and call your canvas e.g. "!canvas" in specialHTMLTargets, createContext seemingly won't be able to find it.