Fix tagged template literal with unicode

[pfgithub]

What does this PR do?

Fixes #8745

console.log(String.raw`æ™`); // -> "æ™" instead of "\u00E6\u2122"

Changes ascii_only to prefers_ascii. It will try to emit mostly ascii, but if a non-ascii character is encountered in a tagged template, it will emit it. Updates execution to scan the file to see if it contains any non-ascii and if it does, load it as utf-8 instead.

This should be benchmarked to see what the performance cost is.

TODO:

• Store the file as utf-16 in the runtime transpiler cache (caches large transpiled files)
• Store the file as utf-16 in the standalone module graph (for bun --compile)
• Figure out what to do about a comment containing a non-ascii characters. Should they mark the whole file as non-ascii, or should the non-ascii characters be removed from the output, or should the bytes be passed to JavascriptCore as latin-1 if it's only a comment? A non-ascii comment is probably much more likely than a non-ascii character within a tagged template literal.

[robobun]

❌ @pfgithub, your commit 66eae13 has 4 failures in #5889:

test/js/web/fetch/fetch.stream.test.ts - 1 failing on 🍎 x64

test/js/bun/http/serve.test.ts - 1 failing on 🍎 x64

test/js/node/net/node-net-server.test.ts - 1 failing on 🪟 x64-baseline

test/js/node/test/parallel/child-process-exec-timeout-kill.test.js - 1 failing on 🍎 aarch64