Web: async improvements #6527

Job	Run time
Check formatting	12s
Minimize JavaScript	9s
Run cargo-deny on Android	21s
Check for typos	5s
Run cargo-deny on iOS	21s
Run cargo-deny on Linux	20s
Test stable Windows 64bit MSVC	5m 4s
Run cargo-deny on macOS	21s
Test stable Windows 32bit MSVC	5m 40s
Run cargo-deny on Redox OS	27s
Test stable Windows 64bit GNU	4m 14s
Run cargo-deny on Web	23s
Test stable Windows 32bit GNU	4m 34s
Run cargo-deny on Windows	24s
Test stable Linux 32bit	4m 3s
Test stable Linux 64bit	3m 53s
Test stable X11	3m 52s
Test stable Wayland	3m 47s
Test stable Android	3m 14s
Test stable Redox OS	2m 46s
Test stable macOS	3m 12s
Test stable iOS x86_64	3m 9s
Test stable iOS Aarch64	3m 11s
Test stable Web	3m 10s
Test nightly Windows 64bit MSVC	4m 4s
Test nightly Windows 32bit MSVC	3m 55s
Test nightly Windows 64bit GNU	5m 38s
Test nightly Windows 32bit GNU	4m 21s
Test nightly Linux 32bit	4m 13s
Test nightly Linux 64bit	3m 53s
Test nightly X11	3m 53s
Test nightly Wayland	3m 46s
Test nightly Android	3m 16s
Test nightly Redox OS	2m 45s
Test nightly macOS	3m 12s
Test nightly iOS x86_64	3m 16s
Test nightly iOS Aarch64	3m 13s
Test 1.73 Windows 64bit MSVC	2m 58s
Test 1.73 Windows 32bit MSVC	3m 14s
Test 1.73 Windows 64bit GNU	3m 21s
Test 1.73 Windows 32bit GNU	3m 36s
Test 1.73 Linux 32bit	3m 43s
Test 1.73 Linux 64bit	3m 16s
Test 1.73 X11	2m 59s
Test 1.73 Wayland	2m 58s
Test 1.73 macOS	2m 47s
Test 1.73 iOS x86_64	3m 1s
Test 1.73 iOS Aarch64	2m 46s
Test 1.73 Web	3m 7s
Test 1.73 Android	2m 59s
Test nightly Web	3m 29s
Test nightly Web Atomic	5m 39s
	2h 36m 10s

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