Extract the diagnostic implementation from
runtime/lua/vim/diagnostic.lua into focused internal modules covering
config, display, float rendering, jump/list helpers, namespace and
storage management, severity/shared utilities, and statusline support.
Move the builtin handlers into runtime/lua/vim/diagnostic/handlers/ and
keep runtime/lua/vim/diagnostic.lua as the public facade that lazily
dispatches to the split modules. This preserves the external
vim.diagnostic API while making the implementation easier to navigate
and reason about.
AI-assisted: Codex
