Add support for Vim's `gdefault` option which makes the `:substitute`
command replace all matches in a line by default, instead of just the
first match. When enabled, the `/g` flag inverts this behavior.

- Add `vim.gdefault` setting
- Add `:set gdefault`, `:set nogdefault` (and short forms `:set gd`, `:set nogd`)
- Fix handling of multiple `/g` flags so that each one inverts the one before

Closes #36209

Release Notes:

- vim: Add `vim.gdefault` setting to make `/g` (replace all matches in a line) the default for substitutions, along with `:set gdefault` and `:set nogdefault` commands (short forms: `gd`, `nogd`)

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Co-authored-by: dino <dinojoaocosta@gmail.com>