Don't expanding globs if user pass variables.

[WindSoilder]

Description

Fixes: #11912

User-Facing Changes

After this change:

let x = '*.nu'; ^echo $x

will no longer expand glob.
If users still want to expand glob, there are also 3 ways to do this:

# 1. use spread operation with `glob` command
let x = '*.nu'; ^echo ...(glob $x)

Tests + Formatting

Done

After Submitting

NaN

[jcfj]

Thank you, this PR fixes a problem I just ran into today (apologies if there's some obvious workaround I'm missing):

The following script executes unreasonably slowly

1..50000 | par-each { mkdir $"foo/($in)" } # 2sec
1..500 | each { $"foo/($in)bar\\*" } | group 10 | each { ^echo ...$in } # 30sec

(The realworld usecase for this is working with nix derivation paths that look like this: /nix/store/zzsylzbjswd9jc47a5yrnlp8bhncnnf9-regex-1.10.2.drv^*.)