test: re-bundle cat on windows (#21255)

The builtin cat was removed in 4bc9229ecb
as it is not used during runtime but only for tests. However, it is a
very small and useful utility program that we need for a lot of our
tests, so there's no harm in bundling it, and it helps us avoid
complicating our build system by having two versions of neovim (neovim
for users and neovim for testing).

Also skip tests if "grep" or "sleep" isn't available.

src/nvim/CMakeLists.txt

@@ -740,6 +740,7 @@ if(WIN32)
   set(EXTERNAL_BLOBS_SCRIPT
     "file(MAKE_DIRECTORY \"${PROJECT_BINARY_DIR}/windows_runtime_deps/platforms\")")
   foreach(DEP_FILE IN ITEMS
+      cat.exe
       curl-ca-bundle.crt
       curl.exe
       diff.exe

test/functional/core/channels_spec.lua

@@ -230,6 +230,7 @@ describe('channels', function()
   end)
 
   it('can use buffered output mode', function()
+    skip(funcs.executable('grep') == 0, 'missing "grep" command')
     source([[
       let g:job_opts = {
       \ 'on_stdout': function('OnEvent'),
@@ -262,6 +263,7 @@ describe('channels', function()
   end)
 
   it('can use buffered output mode with no stream callback', function()
+    skip(funcs.executable('grep') == 0, 'missing "grep" command')
     source([[
       function! OnEvent(id, data, event) dict
         call rpcnotify(1, a:event, a:id, a:data, self.stdout)

test/functional/provider/perl_spec.lua

@@ -9,8 +9,6 @@ local curbufmeths = helpers.curbufmeths
 local insert = helpers.insert
 local expect = helpers.expect
 local feed = helpers.feed
-local is_os = helpers.is_os
-local skip = helpers.skip
 
 do
   clear()
@@ -26,8 +24,6 @@ before_each(function()
 end)
 
 describe('legacy perl provider', function()
-  skip(is_os('win'))
-
   it('feature test', function()
     eq(1, eval('has("perl")'))
   end)
@@ -70,7 +66,6 @@ describe('legacy perl provider', function()
 end)
 
 describe('perl provider', function()
-  skip(is_os('win'))
   teardown(function ()
     os.remove('Xtest-perl-hello.pl')
     os.remove('Xtest-perl-hello-plugin.pl')

test/functional/ui/messages_spec.lua

@@ -16,6 +16,8 @@ local poke_eventloop = helpers.poke_eventloop
 local assert_alive = helpers.assert_alive
 local is_os = helpers.is_os
 local is_ci = helpers.is_ci
+local funcs = helpers.funcs
+local skip = helpers.skip
 
 describe('ui/ext_messages', function()
   local screen
@@ -1916,6 +1918,7 @@ aliquip ex ea commodo consequat.]])
   end)
 
   it('with :!cmd does not crash on resize', function()
+    skip(funcs.executable('sleep') == 0, 'missing "sleep" command')
     feed(':!sleep 1<cr>')
     screen:expect{grid=[[
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