Emscripten: Update HTML shell file from newer releases

[carstene1ns]

[Ghabry]

I diffed the latest emscripten shell against ours and there isn't really anything new.

Except for this bugfix here: emscripten-core/emscripten@1fc1c90#diff-8fd398136d2435d1c53386be85f6ff73
Maybe solves the keyboard focus issue we have in some browsers