Port brew --repository to Bash

[ZhongRuoyu]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

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This provides a significant speedup:

$ hyperfine 'git checkout master; brew --repo homebrew/core' 'git checkout brew-repository-speedup; brew --repo homebrew/core'
Benchmark 1: git checkout master; brew --repo homebrew/core
  Time (mean ± σ):      1.737 s ±  0.388 s    [User: 0.743 s, System: 0.323 s]
  Range (min … max):    1.336 s …  2.438 s    10 runs

Benchmark 2: git checkout brew-repository-speedup; brew --repo homebrew/core
  Time (mean ± σ):     459.1 ms ±  91.9 ms    [User: 100.5 ms, System: 142.1 ms]
  Range (min … max):   366.5 ms … 594.0 ms    10 runs

Summary
  git checkout brew-repository-speedup; brew --repo homebrew/core ran
    3.78 ± 1.13 times faster than git checkout master; brew --repo homebrew/core

[MikeMcQuaid]

Looks good, nice work @ZhongRuoyu!

[olga-mcbfe]

brew --repo homebrew/homebrew used to return /opt/homebrew/Library/Taps/homebrew/homebrew-core and now it returns /opt/homebrew/Library/Taps/homebrew/homebrew-homebrew

[MikeMcQuaid]

@olga-mcbfe The latter seems more correct to me.