Escape value in CSS ~= attribute selector matching

[netliomax25-code]

1. The ~= attribute selector in CssAttributeSelectorItem builds a regex from the selector value, so the value is treated as a pattern instead of a literal word.
2. The value comes from untrusted CSS in an SVG/HTML document, so metacharacters change matching (for example a.c matches abc) and an unbalanced group such as ( throws an unchecked PatternSyntaxException during style resolution.
3. Quoted the value with Pattern.quote before building the pattern, so it matches literally per the CSS ~= semantics.

[iText-CI]

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