feat(secure): add :trust command and vim.secure.trust() (#21107)

Introduce vim.secure.trust() to programmatically manage the trust
database. Use this function in a new :trust ex command which can
be used as a simple frontend.

Resolves: https://github.com/neovim/neovim/issues/21092
Co-authored-by: Gregory Anders <greg@gpanders.com>
Co-authored-by: ii14 <ii14@users.noreply.github.com>

src/nvim/ex_cmds.lua

@@ -2933,6 +2933,12 @@ module.cmds = {
     addr_type='ADDR_OTHER',
     func='ex_tag',
   },
+  {
+    command='trust',
+    flags=bit.bor(EXTRA, FILE1, TRLBAR, LOCK_OK),
+    addr_type='ADDR_NONE',
+    func='ex_trust',
+  },
   {
     command='try',
     flags=bit.bor(TRLBAR, SBOXOK, CMDWIN, LOCK_OK),