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_docmd.c

@@ -1827,6 +1827,7 @@ static bool skip_cmd(const exarg_T *eap)
     case CMD_throw:
     case CMD_tilde:
     case CMD_topleft:
+    case CMD_trust:
     case CMD_unlet:
     case CMD_unlockvar:
     case CMD_verbose: