feat(api): nvim_set_option_value(operation=...) #39849

Problem:
`nvim_set_option_value` cannot "update" options similar to `:set opt=`,
`:set opt+=`, etc. The Lua impls of "vim.opt" / "vim.o" have incomplete,
bespoke reimplementations of those operations.

ref #38420

Solution:
- Add `operation` param to `nvim_set_option_value`, which may be "set",
  "append", "prepend", or "remove".
- Use this feature to implement `vim.opt` / `vim.o`.

runtime/lua/vim/_meta/api.gen.lua

@@ -2305,12 +2305,18 @@ function vim.api.nvim_set_option(name, value) end
 --- @param value any New option value
 --- @param opts vim.api.keyset.option Optional parameters
 --- - buf: Buffer number. Used for setting buffer local option.
+--- - dry_run: (`boolean?`, default: false) If true, then the
+---   option value won't be set.
+--- - operation: One of "set", "append", "prepend", or "remove".
+---   Corresponds to `:set=`, `:set+=`, `:set^=`, and `:set-=`.
+---   Default is "set".
 --- - scope: One of "global" or "local". Analogous to
 --- `:setglobal` and `:setlocal`, respectively.
 --- - tab: `tab-ID` for tab-local options (currently only 'cmdheight'). Tabpage 0
 ---   means the current tabpage. If a non-current tab is given, the value will take
 ---   effect when it is switched-to.
 --- - win: `window-ID`. Used for setting window local option.
+--- @return any # Option value
 function vim.api.nvim_set_option_value(name, value, opts) end
 
 --- Sets a global (g:) variable.

runtime/lua/vim/_meta/api_keysets.gen.lua

@@ -381,7 +381,9 @@ error('Cannot require a meta file')
 
 --- @class vim.api.keyset.option
 --- @field buf? integer
+--- @field dry_run? boolean
 --- @field filetype? string
+--- @field operation? string
 --- @field scope? string
 --- @field tab? integer
 --- @field win? integer