Spec clarifies shorthand use of throw

Other misc changes

• Editorial clarification to the “Throw” clause, explicitly defining “throw” as shorthand for returning ThrowCompletion(...) in algorithm steps.
• Updated several algorithm examples and steps to use the shorthand form instead of spelling out Return ThrowCompletion(...) (including promise, base64/hex, typed array, and call-related steps).
• Headings and explanatory text in the throw section were reworded for consistency.