FP S2973(EscapedUnicodeCharactersCheck) with Unicode Whitespaces

The rule S2973 should not raise issues on escaped white spaces != \u0020 like:

"\u1680 \u180E \u2000 \u200D \u2028 \u2029 \u202F \u205F \u2060 \u3000 \uFEFF"

See SONARJAVA-2794 and Unicode whitespace characters