plugins/table-mode: init - #4567

Description

Adds vim-table-mode (vimPlugins.vim-table-mode), a VimL plugin for creating tables as you type, with automatic re-alignment and commands for converting delimited lines into tables.

Notes for reviewers:

• mkVimPlugin with globalPrefix = "table_mode_"; settingsOptions deliberately not declared per the guidance on freeform settings (option names would have to track the plugin's global set; settingsExample covers the main toggles).
• The plugin's older table_mode_auto_enable/table_mode_disable_ft/table_mode_echo/table_mode_lint globals were removed upstream in 2025, so the description documents the current approach (per-filetype ftplugin/autocommand running :TableModeEnable).

Things done

• Built locally with the targeted test: nix develop --command tests plugins-by-name-table-mode
• nix fmt clean
• Added by-name module + test sources only (auto-imported)

Example enabling in a config:

plugins.table-mode = {
  enable = true;
  settings = {
    auto_align = true;
    disable_mappings = false;
    delimiter = ",";
  };
};