Run bevy systems in wasm even when the tab is not focused

## What problem does this solve or what need does it fill?

It seems like if the user switches to a different tab, the bevy app will basically freeze and stop getting updated.

This seems to be because running the schedule in wasm is tied to `requestAnimationFrame` (https://developer.mozilla.org/en-US/docs/Web/API/window/requestAnimationFrame) calls which are made by winit in the winit_runner.

A potential solution would be:
- if the tab is focused, keep the current scheduling logic
- if the tab is not focused, update the schedule at fixed intervals (for example 60Hz(

Start at the winit_runner scheduling path and read how requestAnimationFrame drives the wasm schedule. Compare focused and unfocused browser behavior, then determine how fixed-interval updates should coexist with the current focused-tab logic. Done means wasm systems continue updating when the tab is unfocused without changing focused-tab scheduling.

Written by the indexing model from the issue text.