test: reorg #15698

Problem:
Subdirectories like "visual", "insert", "normal" encourage people to
separate *related* tests for no good reason.  Typically the _mode_ is
not the relevant topic of a test (and when it is, _then_ create
an appropriate describe() or it()).

Solution:
- Delete the various `test/functional/<mode>/` subdirectories, move
  their tests to more meaningful topics.
- Rename `…/normal/` to `…/editor/`.
  - Move or merge `…/visual/*` and `…/insert/*` tests into here where
    appropriate.
- Rename `…/eval/` to `…/vimscript/`.
  - Move `…/viml/*` into here also.

* test(reorg): insert/* => editor/mode_insert_spec.lua
* test(reorg): cmdline/* => editor/mode_cmdline_spec.lua
* test(reorg): eval core tests => eval_spec.lua

test/functional/vimscript/uniq_spec.lua

@@ -0,0 +1,31 @@
+local helpers = require('test.functional.helpers')(after_each)
+
+local eq = helpers.eq
+local clear = helpers.clear
+local meths = helpers.meths
+local command = helpers.command
+local exc_exec = helpers.exc_exec
+local redir_exec = helpers.redir_exec
+
+before_each(clear)
+
+describe('uniq()', function()
+  it('errors out when processing special values', function()
+    eq('Vim(call):E362: Using a boolean value as a Float',
+       exc_exec('call uniq([v:true, v:false], "f")'))
+  end)
+
+  it('can yield E882 and stop filtering after that', function()
+    command([[
+      function Cmp(a, b)
+        if type(a:a) == type([]) || type(a:b) == type([])
+          return []
+        endif
+        return (a:a > a:b) - (a:a < a:b)
+      endfunction
+    ]])
+    eq('\nE745: Using a List as a Number\nE882: Uniq compare function failed',
+       redir_exec('let fl = uniq([0, 0, [], 1, 1], "Cmp")'))
+    eq({0, {}, 1, 1}, meths.get_var('fl'))
+  end)
+end)