Replace local type declarations for polyfill APIs with those imported from the polyfills.

[bicknellr]

This PR removes the local types describing the polyfill APIs in favor of the new TS externs from the polyfill repos.

• [x] https://github.com/webcomponents/polyfills/pull/457
• [x] Remove local tarball and use released polyfill packages instead.

[github-actions[bot]]

📊 Tachometer Benchmark Results

Summary

callback

• shack: unsure 🔍 -1% - +2% (-0.23ms - +0.57ms)
  ^{this-change vs master}

Results

shack

• Browser: chrome-headless 92.0.4515.107
• Sample size: 330
• Built by: Benchmarks #40
• Commit: a51adb4

Version	Avg time	vs this-change	vs master	vs previous-2.x-release
this-change	24.66ms - 25.20ms	-	unsure 🔍 -1% - +2% -0.23ms - +0.57ms	unsure 🔍 -0% - +2% -0.08ms - +0.61ms
master	24.47ms - 25.06ms	unsure 🔍 -2% - +1% -0.57ms - +0.23ms	-	unsure 🔍 -1% - +2% -0.27ms - +0.46ms
previous-2.x-release	24.46ms - 24.88ms	unsure 🔍 -2% - +0% -0.61ms - +0.08ms	unsure 🔍 -2% - +1% -0.46ms - +0.27ms	-

_{tachometer-reporter-action v2 for Benchmarks}

[bicknellr]

For some reason, I can't add @sorvell as a reviewer.