docs(events): Lua types for autocmd event-data #38518

Problem:
  No LuaLS types for event-data fields (ev.data). Types are only
  documented ad hoc in scattered locations.

Solution:
  Add runtime/lua/vim/_meta/events.lua defining vim.event.<name>.data
  classes for events that provide ev.data. Reference the types from
  each event's help in autocmd.txt, lsp.txt, and pack.txt.

runtime/lua/vim/pack.lua

@@ -175,6 +175,8 @@
 ---- `spec` - plugin's specification with defaults made explicit.
 ---- `path` - full path to plugin's directory.
 ---
+---See `vim.event.packchanged.data` and `vim.event.packchangedpre.data`.
+---
 --- These events can be used to execute plugin hooks. For example:
 ---```lua
 ---local hooks = function(ev)