Web: Implement `MonitorHandle` #6538

Job	Run time
Minimize JavaScript	27s
Check formatting	15s
Run cargo-deny on Android	21s
Run cargo-deny on iOS	21s
Check for typos	7s
Run cargo-deny on Linux	21s
Test stable Windows 64bit MSVC	2m 43s
Run cargo-deny on macOS	22s
Test stable Windows 32bit MSVC	4m 26s
Run cargo-deny on Redox OS	38s
Test stable Windows 64bit GNU	2m 54s
Run cargo-deny on Web	26s
Test stable Windows 32bit GNU	2m 23s
Run cargo-deny on Windows	23s
Test stable Linux 32bit	2m 3s
Test stable Linux 64bit	1m 40s
Test stable X11	1m 34s
Test stable Wayland	1m 41s
Test stable Android	1m 25s
Test stable Redox OS	18s
Test stable macOS	1m 20s
Test stable iOS x86_64	59s
Test stable iOS Aarch64	47s
Test stable Web	1m 27s
Test nightly Windows 64bit MSVC	1m 53s
Test nightly Windows 32bit MSVC	1m 52s
Test nightly Windows 64bit GNU	2m 3s
Test nightly Windows 32bit GNU	1m 54s
Test nightly Linux 32bit	1m 58s
Test nightly Linux 64bit	1m 32s
Test nightly X11	1m 32s
Test nightly Wayland	1m 39s
Test nightly Android	1m 20s
Test nightly Redox OS	35s
Test nightly macOS	1m 4s
Test nightly iOS x86_64	52s
Test nightly iOS Aarch64	56s
Test 1.73 Windows 64bit MSVC	1m 0s
Test 1.73 Windows 32bit MSVC	58s
Test 1.73 Windows 64bit GNU	1m 13s
Test 1.73 Windows 32bit GNU	1m 4s
Test 1.73 Linux 32bit	1m 42s
Test 1.73 Linux 64bit	1m 7s
Test 1.73 X11	54s
Test 1.73 Wayland	55s
Test 1.73 macOS	39s
Test 1.73 iOS x86_64	34s
Test 1.73 iOS Aarch64	33s
Test 1.73 Web	52s
Test 1.73 Android	34s
Test nightly Web	1m 41s
Test nightly Web Atomic	1m 38s
	1h 3m 55s

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