badwords: check indented lines in source code, fix fallouts

- badwords.pl: add `-a` option to check all lines in source code files.
  Before this patch indented lines were skipped (to avoid Markdown code
  fences.)
- GHA/checksrc: use `-a` when verifying the source code.
- GHA/checksrc: disable `So` and `But` rules for source code.
- GHA/checksrc: add docs/examples to the verified sources.
- badwords.txt: delete 4 duplicates.
- badwords.txt: group and sort contractions.
- badwords.txt: allow ` url = `, `DIR`, `<file name`.

Closes #19536

.github/scripts/badwords.pl

@@ -20,7 +20,12 @@ use warnings;
 my @whitelist;
 my %alt;
 my %exactcase;
+my $skip_indented = 1;
 
+if($ARGV[0] eq "-a") {
+    shift @ARGV;
+    $skip_indented = 0;
+}
 my %wl;
 if($ARGV[0] eq "-w") {
     shift @ARGV;
@@ -68,7 +73,7 @@ sub file {
         my $in = $_;
         $l++;
         chomp $in;
-        if($in =~ /^    /) {
+        if($skip_indented && $in =~ /^    /) {
             next;
         }
         # remove the link part