Fixing resize and mouse input coordinates

[zet23t]

Also replacing hardcoded canvas id references with module variable usages

I tested these changes on my somewhat non-standard blog (using different canvas ids and using a different init logic). Testing it with the window flags example is something I want to do before merging this.

[zet23t]

All right. I will try your test in my setup to see how it behaves on my machine and in my non standard setup. Eventually there is another hard coded canvas ID somewhere.

[zet23t]

The problems start when embedding the canvas into a website and enabling the resizable flag.

    SetConfigFlags(FLAG_WINDOW_RESIZABLE);

See the gif how the provided test behaves, when setting that flag. I will also add a test for embedded canvas elements, I think there are then issues with fullscreen modes too.