Bazel: add an installer shortcut to codeql_pack

This makes the first `codeql_pack` in a package add an `installer` target
aliasing the `<name>-installer` one. This makes it so that one can for
example do `bazel run //rust:installer` instead of the stuttering
`bazel run //rust:rust-installer`. If a bazel package defines multiple
`codeql_pack` targets, the first one only will get the `installer` alias.

rust/BUILD.bazel

@@ -56,10 +56,10 @@ codeql_pkg_files(
         pack_prefix = "/".join(parts),
     )
     for parts in (
+        ["rust"],
         [
             "experimental",
             "rust",
         ],
-        ["rust"],
     )
 ]