`set_bookmarks_gs()` old bookmark disabling no longer works with `ghostscript` v10.3

[trevorld]

• This seems to be due to some deliberate changes to break functionality to make it more "secure": https://ghostscript.readthedocs.io/en/gs10.03.0/News.html

(10.03.0) Almost all the "internal" PostScript procedures defined during the interpreter startup are now "executeonly", further reducing the attack surface of the interpreter.

The nature of these procedures means there should be no impact for legitimate usage, but it is possible it will impact uses which abuse the previous accessibility (even for legitimate reasons). Such cases may now require "DELAYBIND", See DELAYBIND

• Not entirely sure how to update postscript/ghostscript code to handle these breaking changes if still possible to do so
• Old bookmarks seem to still be disabled by set_bookmarks_pdftk()
• Bookmarks are still disabled with ghostscript v9.55

[trevorld]

• If you have installed newer/older version of ghostscript in temporary directory can tell {xmpdf} to use it by setting Sys.setenv(R_GSCMD="/path/to/gs")