Alias expansion not implemented

[chaliy]

Description

Alias definition and expansion are not implemented. All 15 alias tests are skipped.

Scope

• alias name='value' - define alias
• unalias name - remove alias
• unalias -a - remove all aliases
• alias (no args) - list all aliases
• shopt -s expand_aliases - enable expansion (bash default in scripts is off)
• Alias expansion of first word in command position
• Trailing space in alias triggers expansion of next word
• Recursive alias expansion
• Alias with variable expansion (variables evaluated at use-time, not definition)
• Alias in subshell and command substitution

Repro

shopt -s expand_aliases
alias hi='echo hello world'
hi
# bashkit outputs: (command not found error)
# expected: hello world

alias echo='echo foo'
echo bar
# expected: foo bar

Test coverage

15 skipped tests in crates/bashkit/tests/spec_cases/bash/alias.test.sh (PR #351).

Oils reference: https://github.com/oilshell/oil/blob/master/spec/alias.test.sh