Fix invalid utf8 slicing in EscapeQuotedString

This could previously panick with multi-byte utf8 characters:

datafusion-sqlparser-rs-896df239ce2264c8/847ddf3/src/ast/value.rs:583:53:
end byte index 271 is not a char boundary; it is inside '�' (bytes 270..273 of string)

Author: Mrmaxmeier

src/ast/value.rs

@@ -577,7 +577,8 @@ impl fmt::Display for EscapeQuotedString<'_> {
                             // The quote is not escaped.
                             // Including idx in the range, so the quote at idx will be printed twice:
                             // in this call to write_str() and in the next one.
-                            f.write_str(&self.string[start_idx..=idx])?;
+                            let end_idx = idx + ch.len_utf8();
+                            f.write_str(&self.string[start_idx..end_idx])?;
                             start_idx = idx;
                         }
                     }