Iterate strings by code point in for loops

[Shaisolaris]

{{ for c of "..." }} turns a string into items with item.split(""), which splits by UTF-16 code unit. Characters outside the BMP (emoji, many CJK extension characters) come out as two lone surrogates:

{{ for c of "a😀b" }}{{ c }}-{{ /for }}

renders a-\ud83d-\ude00-b- (two broken characters) instead of a-😀-b-. Keys from for key, c of ... are shifted the same way. A String object already iterates by code point because it goes through the Symbol.iterator branch, so primitives and objects behave differently today.

This uses Array.from(item), which iterates the way JavaScript's own for...of does. ASCII and other BMP strings produce the same items and keys as before.

Tests: two cases added to "For tag (string)" in test/for.test.ts. They fail on main and pass with the change. deno test --allow-read test gives 105 passed, 0 failed (3 ignored), and deno fmt --check and deno lint are clean. I also added an Unreleased entry to CHANGELOG.md; happy to drop it if you prefer to write those yourself.

[oscarotero]

I knew this limitation but didn't know that Array.from() could fix it. That's great, thank you!