feat: add sort_by "filetype"

[moniquelive]

Fixes #2288 by proposing a new kind of sorting: by vim's filetype.

[alex-courtis]

Thank you for your contibution!

This somewhat works however we're at the mercy of filesystem/discovery ordering.

rm * ; touch 20.yaml 30.toml 40.cpp 41.cpp 10.zig 35.nothing 25.nothing

     20.yaml
     10.zig
     25.nothing
     30.toml
     35.nothing
     40.cpp
     41.cpp

rm * ; touch 20.yaml 30.toml 40.cpp 41.cpp 10.zig 35.nothing 25.nothing 21.nothing

     40.cpp
     41.cpp
     30.toml
     20.yaml
     10.zig
     21.nothing
     25.nothing
     35.nothing

Please:

• add a fallback for the whatever cases - I think name is best.

I'd be grateful if you could add the same fallback to extension however that can be a subsequent PR.

[alex-courtis]

sorters.lua merge sort is complex, added for performance reasons #334

Being mindful of Chesterton's fence it might be time to simplify to drop back to the basic quick sort table.sort

[alex-courtis]

Works nicely:

rm -rf * ; touch 20.yaml 30.toml 40.cpp 41.cpp 10.zig 35.nothing 25.nothing ; mkdir -p 15/a ; touch 15/a/10.toml 15/a/20.nothing 15/a/10.yaml

  ~/2302/..                   │
    15/a                    │~
       10.toml               │~
       10.yaml               │~
       20.nothing            │~
     40.cpp                  │~
     41.cpp                  │~
     30.toml                 │~
     20.yaml                 │~
     10.zig                  │~
     25.nothing              │~
     35.nothing              │~