The code in pre.js and engine.js is a bit confusing to see in isolation, since the files aren't valid JS files by themselves. This just adds some explanatory text to both files. Fixes #22937. (cherry picked from commit 61d5513525)
61d5513525
(cherry picked from commit 63c7fc6358)
63c7fc6358
Since WebGL 2.0 is required, requiring WebAssembly support as well has little impact on compatibility.