Fix spec typos and logical ambiguities

[Djuffin]

I have corrected several typos, spelling mistakes, and logical ambiguities in the specification text.

Key changes include:

1. Removed a duplicate "in" in avc_codec_registration.src.html.
2. Clarified construction loops in index.src.html where the [[Detached]] internal slot check was ambiguous, explicitly linking it to the |transferable| being iterated.
3. Standardized the phrasing of the "Create a VideoFrame" algorithm to match the rest of the document.
4. Fixed a smart quote and added missing periods in algorithm steps for better consistency.
5. Verified all changes by building the spec via the Bikeshed API.

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PR created automatically by Jules for task 1603028004291981030 started by @Djuffin

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