Compat: Add 'isPropagationStopped' fn to event

[reznord]

Adds 'isPropagationStopped' function to events.

Let me know if I missed something.

Super simple first contribution. 🙈

[github-actions]

Size Change: +54 B (0%)

Total Size: 38.4 kB

Filename	Size	Change
compat/dist/compat.js	3.07 kB	+17 B (0%)
compat/dist/compat.module.js	3.09 kB	+19 B (0%)
compat/dist/compat.umd.js	3.12 kB	+18 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
debug/dist/debug.js	2.98 kB	0 B
debug/dist/debug.module.js	2.96 kB	0 B
debug/dist/debug.umd.js	3.04 kB	0 B
devtools/dist/devtools.js	175 B	0 B
devtools/dist/devtools.module.js	185 B	0 B
devtools/dist/devtools.umd.js	252 B	0 B
dist/preact.js	3.73 kB	0 B
dist/preact.min.js	3.73 kB	0 B
dist/preact.module.js	3.75 kB	0 B
dist/preact.umd.js	3.79 kB	0 B
hooks/dist/hooks.js	1.05 kB	0 B
hooks/dist/hooks.module.js	1.08 kB	0 B
hooks/dist/hooks.umd.js	1.13 kB	0 B
test-utils/dist/testUtils.js	390 B	0 B
test-utils/dist/testUtils.module.js	392 B	0 B
test-utils/dist/testUtils.umd.js	469 B	0 B

_{compressed-size-action}

[coveralls]

Coverage increased (+0.0004%) to 99.792% when pulling 9a85d39 on propogation-stopped into 066f3d0 on master.