feat(runtime/health): support lua healthchecks

- Refactor health.vim to discover lua healthcheck in the runtime
  directories lua/**/health{/init}.lua
- Support healthchecks for lua submodules e.g :checkhealth vim.lsp and
  also support wildcard "*" at the end for all submodules
  :checkhealth vim*
- Refactor health.vim to use variable scope instead of output capturing
- Create health.lua module to wrap report functions and future
  extensibility.
- Move away from searching just in the runtimepath, use
  `nvim_get_runtime_file` due to #15632

Example:
Plugin linter in rtp can declare it's checkhealts in lua module
`lua/linter/health{/init}.lua` that returns a table with a method
"check" that when executed calls the report functions provided by the
builtin lua module require("health").

The plugin also has a submodule `/lua/linter/providers` in which it
defines `/lua/linter/providers/health{/init}.lua`

This plugin healthcheck can now be run by the ex command:
  `:checkhealth linter linter.providers`

Also calling all submodules can be done by:
  `:checkhealth linter*

And "linter" and "linter.provider" would be discovered when:
  `:checkhealth`

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