fix(provider): misleading :checkhealth if user sets g:loaded_python3_provider=1 #32696

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.

(cherry picked from commit b4906577c9)

Co-authored-by: Sathya Pramodh <94102031+sathya-pramodh@users.noreply.github.com>

runtime/autoload/provider/clipboard.vim

@@ -5,11 +5,11 @@
 if exists('g:loaded_clipboard_provider')
   finish
 endif
-" Default to 1.  provider#clipboard#Executable() may set 2.
+" Default to 0.  provider#clipboard#Executable() may set 2.
 " To force a reload:
 "   :unlet g:loaded_clipboard_provider
 "   :runtime autoload/provider/clipboard.vim
-let g:loaded_clipboard_provider = 1
+let g:loaded_clipboard_provider = 0
 
 let s:copy = {}
 let s:paste = {}
@@ -284,4 +284,4 @@ function! provider#clipboard#Call(method, args) abort
 endfunction
 
 " eval_has_provider() decides based on this variable.
-let g:loaded_clipboard_provider = empty(provider#clipboard#Executable()) ? 1 : 2
+let g:loaded_clipboard_provider = empty(provider#clipboard#Executable()) ? 0 : 2

runtime/autoload/provider/node.vim

@@ -1,7 +1,7 @@
 if exists('g:loaded_node_provider')
   finish
 endif
-let g:loaded_node_provider = 1
+let g:loaded_node_provider = 0
 
 function! s:is_minimum_version(version, min_version) abort
   if empty(a:version)
@@ -152,7 +152,7 @@ endfunction
 
 let s:err = ''
 let [s:prog, s:_] = provider#node#Detect()
-let g:loaded_node_provider = empty(s:prog) ? 1 : 2
+let g:loaded_node_provider = empty(s:prog) ? 0 : 2
 
 if g:loaded_node_provider != 2
   let s:err = 'Cannot find the "neovim" node package. Try :checkhealth'

runtime/autoload/provider/perl.vim

@@ -11,5 +11,5 @@ function! provider#perl#Require(host) abort
 endfunction
 
 let s:prog = v:lua.vim.provider.perl.detect()
-let g:loaded_perl_provider = empty(s:prog) ? 1 : 2
+let g:loaded_perl_provider = empty(s:prog) ? 0 : 2
 call v:lua.require'vim.provider.perl'.start()

runtime/autoload/provider/python3.vim

@@ -11,5 +11,5 @@ function! provider#python3#Require(host) abort
 endfunction
 
 let s:prog = v:lua.vim.provider.python.detect_by_module('neovim')
-let g:loaded_python3_provider = empty(s:prog) ? 1 : 2
+let g:loaded_python3_provider = empty(s:prog) ? 0 : 2
 call v:lua.require'vim.provider.python'.start()

runtime/autoload/provider/ruby.vim

@@ -11,6 +11,6 @@ function! provider#ruby#Call(method, args) abort
 endfunction
 
 let s:prog = v:lua.vim.provider.ruby.detect()
-let g:loaded_ruby_provider = empty(s:prog) ? 1 : 2
+let g:loaded_ruby_provider = empty(s:prog) ? 0 : 2
 let s:plugin_path = expand('<sfile>:p:h') . '/script_host.rb'
 call v:lua.require'vim.provider.ruby'.start(s:plugin_path)