Preprocessor update

– Macroprocessor: print line numbers in the output of @#echomacrovars (without “save” option)
– Correctly handle whitespaces when parsing contents of legacy “mcp” tags
– Misc simplifications and C++20 modernizations

preprocessor @ 05047fd4

-Subproject commit f9e91d339a141dd72205d032060b1032bfc446cd
+Subproject commit 05047fd45fdf23ebab727150fbb3522b56650bde