Problem:
:checkhealth shows a confusing message if user sets
g:loaded_python3_provider=1.

Solution:
- Show a warning if that var is set to 1.
- Update provider modules to default to 0. Any user code that is
  checking for 1, is like already broken because these may be set to 2.

Problem:

    Node.js provider (optional) ~
    - ERROR Failed to run healthcheck for "provider.node" plugin. Exception:
      …/runtime/lua/provider/node/health.lua:9: attempt to call field 'provider_disabled' (a nil value)

    Perl provider (optional) ~
    - ERROR Failed to run healthcheck for "provider.perl" plugin. Exception:
      …/runtime/lua/provider/perl/health.lua:8: attempt to call field 'provider_disabled' (a nil value)

    Python 3 provider (optional) ~
    - ERROR Failed to run healthcheck for "provider.python" plugin. Exception:
      …/runtime/lua/provider/python/health.lua:226: attempt to call field 'provider_disabled' (a nil value)

    Ruby provider (optional) ~
    - ERROR Failed to run healthcheck for "provider.ruby" plugin. Exception:
      …/runtime/lua/provider/ruby/health.lua:9: attempt to call field 'provider_disabled' (a nil value)

Solution:
Add these files to the runtime sanity check.

fix #29302

Unlike vim.fn.expand(), vim.fs.normalize() doesn't expand wildcards.

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.*`.