vim: fix config and runtime

vim: fix config and runtime

- Install shared runtime for both full and fuller.
- Switch big to huge as big is just an alias to normal.
- Fix default config path for tiny variant.
- Use upstream default config for both full and fuller.
- Don't mark default config files for backup.
- Don't mix variant files.
- Mark fuller variant config files for backup.
- Update configure arguments and remove deprecated ones.
- Remove deprecated configuration variables.
- Improve descriptions.
- Fix the following error by installing the missing runtime files for
  full and correctly installing the default config for tiny:

  E1187: Failed to source defaults.vim

- Fix the following fuller error by installing the missing directory in
  runtime:

  Error detected while processing /usr/share/vim/vim91/plugin/netrwPlugin.vim:
  line    7:
  E919: Directory not found in 'packpath': "pack/*/opt/netrw"

Fixes: https://github.com/openwrt/packages/issues/20203
Fixes: https://github.com/openwrt/packages/issues/28104
Signed-off-by: George Sapkin <george@sapk.in>