Matter: encode strings longer than 255 bytes (#25185)

Matter_TLV.tlv2raw() wrote a UTF2 string with bytes().frostring(), a
typo for fromstring(), so encoding any string of more than 255 bytes
(which is given type UTF2 automatically) raised attribute_error.

lib/libesp32/berry_matter/src/embedded/Matter_TLV.be

@@ -375,7 +375,7 @@ class Matter_TLV
       elif self.typ == 0x0D #-TLV.UTF2-#
         if size(self.val) > 65535 raise "value_error", "string too big" end
         b.add(size(self.val), 2)
-        b..bytes().frostring(str(self.val))
+        b..bytes().fromstring(str(self.val))
       elif self.typ == 0x10 #-TLV.B1-#
         if size(self.val) > 255 raise "value_error", "bytes too big" end
         b.add(size(self.val), 1)