runtime(dist): centralize safe executable check and add vim library (#13413)

Follow up to 816fbcc26 (patch 9.0.1833: [security] runtime file fixes,
2023-08-31) and f7ac0ef50 (runtime: don't execute external commands when
loading ftplugins, 2023-09-06).

This puts the logic for safe executable checks in a single place, by introducing
a central vim library, so all filetypes benefit from consistency.

Notable changes:
- dist#vim because the (autoload) namespace for a new runtime support
  library. Supporting functions should get documentation. It might make
  life easier for NeoVim devs to make the documentation a new file
  rather than cram it into existing files, though we may want
  cross-references to it somewhere…
- The gzip and zip plugins need to be opted into by enabling execution
  of those programs (or the global plugin_exec). This needs
  documentation or discussion.
- This fixes a bug in the zig plugin: code setting s:tmp_cwd was removed
  in f7ac0ef50 (runtime: don't execute external commands when loading
  ftplugins, 2023-09-06), but the variable was still referenced. Since
  the new function takes care of that automatically, the variable is no
  longer needed.

Signed-off-by: D. Ben Knoble <ben.knoble+github@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/runtime/ftplugin/changelog.vim b/runtime/ftplugin/changelog.vim
index a62433378a..ab73949be5 100644
--- a/runtime/ftplugin/changelog.vim
+++ b/runtime/ftplugin/changelog.vim
@@ -57,8 +57,8 @@ if &filetype == 'changelog'
     endif
     let s:default_login = 'unknown'
 
-    " Disabled by default for security reasons.  
-    if get(g:, 'changelog_exec', get(g:, 'plugin_exec', 0))
+    " Disabled by default for security reasons.
+    if dist#vim#IsSafeExecutable('changelog', 'whoami')
       let login = s:login()
     else
       let login = s:default_login