[Tags] Use 'readtags' if query string is given

This pre-filtering is critical when working with large tag files.

'readtags' can perform a binary search for the given prefix string
but fzf has to load the entire file into memory just to start searching.

Close #1529
Close #1524

bin/tags.pl

@@ -2,8 +2,16 @@
 
 use strict;
 
+my $prefix = shift @ARGV;
+
 foreach my $file (@ARGV) {
-  open my $lines, $file;
+  my $lines;
+  if ($prefix eq "") {
+    open $lines, $file;
+  } else {
+    # https://perldoc.perl.org/perlopentut#Expressing-the-command-as-a-list
+    open $lines, '-|', 'readtags', '-t', $file, '-e', '-p', $prefix;
+  }
   while (<$lines>) {
     unless (/^\!/) {
       s/^[^\t]*/sprintf("%-24s", $&)/e;