Emscripten: FPS counter broke, showing more than 60 fps

The web player FPS counter which appears whith the F2 key regressed likely since major changes allowing frameskip and fast forward since WebAssembly landed.
Ideally, should get a count similar to JavaScript's requestAnimationFrame, which is based on system refresh rate.

[Ghabry]

Here for comparison:
As you know we use Asynchify right now because the normal animation frame API had problems with frameskip.
With the Clock refactor this was mostly solved (But I still get a browser freeze when 0 FPS are reached)

With Asyncify:
https://easyrpg.org/play/test/gabriel/easyrpg-player.html
https://easyrpg.org/play/test/gabriel/easyrpg-player.html?game=frozen_triggers

Without (correct frame counter):
https://easyrpg.org/play/test/gabriel2/easyrpg-player.html
https://easyrpg.org/play/test/gabriel2/easyrpg-player.html?game=frozen_triggers

Please also check, besides looking at the frame counter, what feels "smoother" for you.

Also added a fix for our easteregg (#1899)

Imo the version with Asyncify feels less choppy. The one without sometimes hangs for short moments.

Frozen Triggers desktop test, I feel the scroll while displacing between the snowy weather and the cavern smoother in the "Without" version. It jumps slightly more with the Asyncify version here. (Firefox on Ryzen 5 2400G on Fedora 34 GNOME 40)

Frozen Triggers mobile test, with Asynficy: bad performance as expected, maybe 4 fps. But without Asyncify it gets even worse: not even loading the snow or audio, slow asset loading, even slower FPS. (Firefox on a low end quad core mediatek Android Go potatophone 1 gb ram)

Testgame scrolling works smoother to me on both desktop and mobile without asyncify, so it seems the frozen triggers issue on mobile is related to the 0fps somehow.

[Ghabry]

Also pinging the others:
@carstene1ns @rueter37 @fmatthew5876

Could you please compare the Async vs. No async version on both your Computer and your Smartphone and tell me which feels "smoother". This is highly subjective so we must find consense first.

The Asyncify version is way smoother for me than the no async version. Tested the desktop versions, because due to not possessing a smartphone I could not test the mobile versions.

Desktop PC specs:
Browser: Firefox 88.0
OS: Lubuntu 20.04
CPU: Intel Core i5-4670K
RAM: 16 GB