nixos/bash: Use escapeShellArg for shell aliases

This patch uses the library function `lib.escapeShellArg` to improve
the handling of shell aliases in the NixOS module `bash`, copying the
corresponding change made to the `zsh` module in commit
1e211a70cbdaf230a18ea4cb67a959039d5c2ddb (for which GitHub pull
request #47471 was filed).

This patch resolves GitHub issue #16973.

This change presumably also should be copied to the `fish` module, but
I don't know `fish` syntax so that won't be done by me.

GitHub: Close NixOS/nixpkgs#16973.

nixos/modules/programs/bash/bash.nix

@@ -33,7 +33,7 @@ let
   '';
 
   bashAliases = concatStringsSep "\n" (
-    mapAttrsFlatten (k: v: "alias ${k}='${v}'") cfg.shellAliases
+    mapAttrsFlatten (k: v: "alias ${k}=${escapeShellArg v}") cfg.shellAliases
   );
 
 in