Fix hydrating textarea with value prop

[andrewiggins]

If a component rendered <textarea value="Test" />, on the server we'd render <textarea>Test</textarea>, but on the client when hydrating, we'd remove the children of <textarea> since the component didn't specify any (textarea value="test" />). Further, since we don't set attributes or properties on hydration, the value property doesn't get applied either.

This PR fixes this behavior by adding a new hook to compat which checks if the VNode is a textarea and always applying the value if the DOM value doesn't match.

[coveralls]

Coverage: 99.548% (+0.004%) from 99.543% when pulling aeb1e77 on hydrate-textarea into dec4d42 on master.

[github-actions]

Size Change: +204 B (0%)

Total Size: 54.2 kB

Filename	Size	Change
compat/dist/compat.js	3.88 kB	+69 B (1%)
compat/dist/compat.module.js	3.81 kB	+66 B (1%)
compat/dist/compat.umd.js	3.94 kB	+69 B (1%)

ℹ️ View Unchanged

Filename	Size	Change
debug/dist/debug.js	3 kB	0 B
debug/dist/debug.module.js	3.01 kB	0 B
debug/dist/debug.umd.js	3.08 kB	0 B
devtools/dist/devtools.js	231 B	0 B
devtools/dist/devtools.module.js	240 B	0 B
devtools/dist/devtools.umd.js	314 B	0 B
dist/preact.js	4.23 kB	0 B
dist/preact.min.js	4.26 kB	0 B
dist/preact.min.module.js	4.26 kB	0 B
dist/preact.min.umd.js	4.28 kB	0 B
dist/preact.module.js	4.25 kB	0 B
dist/preact.umd.js	4.31 kB	0 B
hooks/dist/hooks.js	1.49 kB	0 B
hooks/dist/hooks.module.js	1.52 kB	0 B
hooks/dist/hooks.umd.js	1.57 kB	0 B
jsx-runtime/dist/jsxRuntime.js	360 B	0 B
jsx-runtime/dist/jsxRuntime.module.js	326 B	0 B
jsx-runtime/dist/jsxRuntime.umd.js	441 B	0 B
test-utils/dist/testUtils.js	442 B	0 B
test-utils/dist/testUtils.module.js	444 B	0 B
test-utils/dist/testUtils.umd.js	526 B	0 B

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[marvinhagemeister]

LGTM, one minor question but feel free to merge