Emscripten produces very large binaries at the default "-g" debug level

Building a small Qt example using at various build levels gives the following .wasm file sizes and link times. (em++ 2.0.31)

```
-g1 29 MB 8 s
-g2 29 MB 8 s
-g3 112 MB 22 s
-g 112 MB 22 s
-Os 12 MB 19 s
```

To give an idea of the true size of the example, compressing the -Os build with brotli gives a 2.6MB binary.

Could Emscripten's default debug output at "-g" be changed to correspond to "-g2" instead of "-g3"? In my experience -g2 provides enough debug output for many use cases (mainly symbolicated stack traces), while still allowing for a relatively fast edit/debug cycle.