refactor(checkhealth)!: rename to vim.health, move logic to Lua #18720

- Complete function:
  There was lots of unnecessary C code for the complete function, therefore
  moving it to Lua and use all the plumbing we have in place to retrieve the
  results.
- Moving the module:
  It's important we keep nvim lua modules name spaced, avoids conflict with
  plugins, luarocks, etc.

test/functional/fixtures/lua/test_plug/submodule_failed/health.lua

@@ -1,10 +1,9 @@
 local M = {}
-local health = require("health")
 
 M.check = function()
-  health.report_start("report 1")
-  health.report_ok("everything is fine")
-  health.report_warn("About to add a number to nil")
+  vim.health.report_start("report 1")
+  vim.health.report_ok("everything is fine")
+  vim.health.report_warn("About to add a number to nil")
   local a = nil + 2
   return a
 end