:ls : show "R", "F" for terminal-jobs #10370

This matches Vim behavior. From `:help :ls` :

    R    a terminal buffer with a running job
    F    a terminal buffer with a finished job
    ?    a terminal buffer without a job: `:terminal NONE`

TODO: implement `:terminal NONE`.

ref #10349

test/functional/ex_cmds/ls_spec.lua

@@ -0,0 +1,33 @@
+local helpers = require('test.functional.helpers')(after_each)
+local clear = helpers.clear
+local command = helpers.command
+local eq = helpers.eq
+local eval = helpers.eval
+local feed = helpers.feed
+local retry = helpers.retry
+
+describe(':ls', function()
+  before_each(function()
+    clear()
+  end)
+
+  it('R, F for :terminal buffers', function()
+    command('edit foo')
+    command('set hidden')
+    command('terminal')
+    command('vsplit')
+    command('terminal')
+    feed('iexit<cr>')
+    retry(nil, 5000, function()
+      local ls_output = eval('execute("ls")')
+      -- Normal buffer.
+      eq('\n  1  h ', string.match(ls_output, '\n *1....'))
+      -- Terminal buffer [R]unning.
+      eq('\n  2 #aR', string.match(ls_output, '\n *2....'))
+      -- Terminal buffer [F]inished.
+      eq('\n  3 %aF', string.match(ls_output, '\n *3....'))
+    end)
+  end)
+
+end)
+