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
1e211a70 (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.