Add text_length (length of text) to zint_symbol, and new

`BARCODE_PLAIN_HRT` option for `output_options` - for use
  primarily by ZXing-C++ but may be generally useful;
  centralize setting of HRT using new common `hrt_cpy_nochk()` etc.
  routines to ensure `text_length` always set
PLESSEY: add show default check characters option
CODE32: ignore `option_2` (check digit options)
PZN: ignore `option_2` (check digit options) except when indicates
  PZN7 only
DPD: exclude DEL from ident tag also
out_maybe_mkdir: fix `utf8_to_wide()` return (Windows only)
general: replace use of `strcpy()` etc. (except for test suite)
  with `memcpy()`, `hrt_()` etc. in lib & `cpy_str()` etc. in CLI
  & `cpy_bytearray_left()` in backend_qt
clang-tidy: update README reflecting above
backend_tcl: use sizeof(primary) to check length; tabs -> spaces
general: various code fiddling
docs: pandoc 3.6.2 -> 3.6.3

frontend_qt/frontend_qt.pro

@@ -52,6 +52,7 @@ FORMS += extCLI.ui \
          grpMQR.ui \
          grpMSICheck.ui \
          grpPDF417.ui \
+         grpPlessey.ui \
          grpPZN.ui \
          grpQR.ui \
          grpRMQR.ui \