Make `safeId()` more robust.

[nexushoratio]

Characters like ( and ) break things.

[nexushoratio]

The web API CSS.escape() looks like a suitable alternative.

It make make sense to simply retire this function.

[nexushoratio]

The need for escaping is inconsistent.

Specifically, for the problem that inspired this, the name of the class in the style element does need to be escaped, but not in the element's classList.

Since we do not need to unescape these values, keeping safeId() may be a better idea after all, so that the same safe strings are used everywhere. But we do need something more scalable than the current hand crafting.

Likely, keep :alnum:, and replace everything else with... something.

[nexushoratio]

Maybe something like:

s.replace(/[^\w .]/gu, (c) => `x${c.charCodeAt(0).toString(16)}`)
  .replaceAll(' ', '-')
  .replaceAll('.', '_')

Should run some tests to verify what happens with certain emoji strings and Unicode surrogates.

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