tests/data: move --libcurl output to external data files

To make the test files XML-compliant, and the expected results
possibly easier to manage by keeping them in `.c` files.

Non-XML-compliant files are down to 36 after this patch.

Also:
- make all macro expansions apply to `%includetext` contents.

Closes #19799

scripts/checksrc-all.pl

@@ -22,6 +22,7 @@ if(@ARGV) {
 }
 
 @files = grep !/\/CMakeFiles\//, @files;
+@files = grep !/tests\/data\/data.+\.c/, @files;
 @files = map { dirname($_) } @files;
 my @dirs = sort { $a cmp $b } keys %{{ map { $_ => 1 } @files }};