The scan that decides whether a program uses a web stream operation the
native streams lack only matched property accesses, so a TypeScript
program whose one such operation was `body["tee"]()` kept the native
streams and threw a TypeError at the call. Element accesses with a string
literal key now count the same way, in the TypeScript scan and in the
JavaScript one.
Adds the corpus program web-streams-typed-element-tee.ts, with its corpus
cost and order baseline.
Chris Tate
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