Fix couch_debug:opened_files* functions

[nickva]

They relied on scanning async IO thread pool ports (efile) before . That only worked in Erlang versions < 21. Since then file IO was moved to dirty schedulers so listing efile ports doesn't yield any useful results.

The partial fix is iterate through processes() and pick out the ones for which couch_file has put anything into the process dictionary. This will skip non-couch-file files but it's probably still better than nothing.

[nickva]

Example of usage:

(node1@127.0.0.1)1> couch_debug:opened_files().
[{<0.417.0>,
  {file_descriptor,prim_file,
                   #{handle => #Ref<0.3584905603.118358043.227800>,
                     owner => <0.417.0>,r_ahead_size => 0,
                     r_buffer => #Ref<0.3584905603.118358017.227799>}},
  "/Users/nvatama/asf/dev/lib/node1/data/_nodes.couch"},
 {<0.434.0>,
  {file_descriptor,prim_file,
                   #{handle => #Ref<0.3584905603.118358046.228058>,
                     owner => <0.434.0>,r_ahead_size => 0,
                     r_buffer => #Ref<0.3584905603.118358017.227932>}},
  "/Users/nvatama/asf/dev/lib/node1/data/_dbs.couch"},
 ...

(node1@127.0.0.1)3> couch_debug:opened_files_contains("_replicator").
[{<0.790.0>,
  {file_descriptor,prim_file,
                   #{handle => #Ref<0.3584905603.118358045.227768>,
                     owner => <0.790.0>,r_ahead_size => 0,
                     r_buffer => #Ref<0.3584905603.118358018.227921>}},
  "/Users/nvatama/asf/dev/lib/node1/data/shards/00000000-7fffffff/_replicator.1655761414.couch"},

 couch_debug:opened_files_by_regexp(".*_replicator.*").
[{<0.790.0>,
  {file_descriptor,prim_file,
                   #{handle => #Ref<0.3584905603.118358045.227768>,
                     owner => <0.790.0>,r_ahead_size => 0,
                     r_buffer => #Ref<0.3584905603.118358018.227921>}},
  "/Users/nvatama/asf/dev/lib/node1/data/shards/00000000-7fffffff/_replicator.1655761414.couch"},

[jaydoane]

Seems to work as expected:

(node1@127.0.0.1)8> length(couch_debug:opened_files()).
132

(node1@127.0.0.1)9> length(couch_debug:opened_files_contains("_global_change")).
8

(node1@127.0.0.1)10> length(couch_debug:opened_files_by_regexp(".*_global.*")).
8