JavaScript formatter

This is a token scanner, not a parser. Strings, template literals (including ${...} expressions), regex literals, and comments are copied through verbatim, and keywords keep their case. Statements that relied on a newline for automatic semicolon insertion after return, throw, break, continue, or yield get an explicit semicolon so the output keeps its meaning. A clean run is a good sign, not a guarantee that the code would parse; exotic syntax may come out imperfect.