Automatic update from web-platform-testsFix bugs in split-up encoding tests
Bugs were introduced in d6c29bef8d4bcdfe4f689defca73360b07647d71
* Some script paths were wrong
* A big5 test referenced eucjpEncoder instead of big5Encoder
* That big5 test also referenced encode-form-common.js instead of
encode-href-common.js
Fixes#11015.
Also add code to generate variants.
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wpt-commits: 5e0fea392c570e81ec7932466ac4c142ff83606d
wpt-pr: 11292