refactor!: remove `nvim` and `provider` module for checkhealth

The namespacing for healthchecks for neovim modules is inconsistent and
confusing. The completion for `:checkhealth` with `--clean` gives

```
nvim
provider.clipboard
provider.node
provider.perl
provider.python
provider.ruby
vim.lsp
vim.treesitter
```

There are now three top-level module names for nvim: `nvim`, `provider`
and `vim` with no signs of stopping. The `nvim` name is especially
confusing as it does not contain all neovim checkhealths, which makes it
almost a decoy healthcheck.

The confusion only worsens if you add plugins to the mix:

```
lazy
mason
nvim
nvim-treesitter
provider.clipboard
provider.node
provider.perl
provider.python
provider.ruby
telescope
vim.lsp
vim.treesitter
```

Another problem with the current approach is that it's not easy to run
nvim-only healthchecks since they don't share the same namespace. The
current approach would be to run `:che nvim vim.* provider.*` and would
also require the user to know these are the neovim modules.

Instead, use this alternative structure:

```
vim.health
vim.lsp
vim.provider.clipboard
vim.provider.node
vim.provider.perl
vim.provider.python
vim.provider.ruby
vim.treesitter
```

and

```
lazy
mason
nvim-treesitter
telescope
vim.health
vim.lsp
vim.provider.clipboard
vim.provider.node
vim.provider.perl
vim.provider.python
vim.provider.ruby
vim.treesitter
```

Now, the entries are properly sorted and running nvim-only healthchecks
requires running only `:che vim.*`.

1 files changed, 39 insertions, 0 deletions

diff --git a/runtime/lua/vim/provider/clipboard/health.lua b/runtime/lua/vim/provider/clipboard/health.lua
new file mode 100644
index 0000000000..e44f7d32cc
--- /dev/null
+++ b/runtime/lua/vim/provider/clipboard/health.lua
@@ -0,0 +1,39 @@
+local health = vim.health
+
+local M = {}
+
+function M.check()
+  health.start('Clipboard (optional)')
+
+  if
+    os.getenv('TMUX')
+    and vim.fn.executable('tmux') == 1
+    and vim.fn.executable('pbpaste') == 1
+    and not health.cmd_ok('pbpaste')
+  then
+    local tmux_version = string.match(vim.fn.system('tmux -V'), '%d+%.%d+')
+    local advice = {
+      'Install tmux 2.6+.  https://superuser.com/q/231130',
+      'or use tmux with reattach-to-user-namespace.  https://superuser.com/a/413233',
+    }
+    health.error('pbcopy does not work with tmux version: ' .. tmux_version, advice)
+  end
+
+  local clipboard_tool = vim.fn['provider#clipboard#Executable']()
+  if vim.g.clipboard ~= nil and clipboard_tool == '' then
+    local error_message = vim.fn['provider#clipboard#Error']()
+    health.error(
+      error_message,
+      "Use the example in :help g:clipboard as a template, or don't set g:clipboard at all."
+    )
+  elseif clipboard_tool:find('^%s*$') then
+    health.warn(
+      'No clipboard tool found. Clipboard registers (`"+` and `"*`) will not work.',
+      ':help clipboard'
+    )
+  else
+    health.ok('Clipboard tool found: ' .. clipboard_tool)
+  end
+end
+
+return M