FieldView.unescaped

Returns the logical text of the field with escapes resolved when needed.

Notes:

• This function may allocate when needsUnescape or needsBackslashUnescape is true, or when a distinct string instance is required. For zero-allocation access to the underlying slice (possibly still containing escapes), use toString().
• Doubled-quote collapsing uses the field's own quoteChar, so fields produced by non-RFC dialects (e.g. `'`) unescape correctly.
• Backslash collapsing applies to `\` before the quote, the delimiter, CR/LF, or another backslash, per the BACKSLASH escape-style contract.