Keep chrome69 downleveling for Android 9 WebViews, but only hard-fail on
logical assignment after transpile. Regex/polyfill feature detects and
minified ternaries can contain `??`/`?.` character sequences that are not
optional chaining or nullish coalescing operators.
Address issues #217#218 and integrate the useful parts of PR #219 without
regressions: stop player rebuild on episode reverse, grid/paged episodes,
poster placeholders, chrome69 client transpile for Amlogic WebView, and
duration-signature ad block detection while keeping interstitial/proxy filters.
Bump to 4.9.15.
kuekhaoyang