bundle/commands/exec: check that Brewfile is installed with --check

[carlocab]

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brew bundle exec behaves correctly only after doing brew bundle install.

Running brew bundle check can be slow, so let's add a --check flag
to brew bundle exec which will also run brew bundle check before
brew bundle exec to ensure that the Brewfile has been installed
before proceeding.

Alternative to #19636 which makes --check the default behaviour. I have a mild
preference for this version since the additional brew bundle check makes
brew bundle env and brew bundle exec true 60% slower.

Another option is to merge #19636 while adding a --no-check flag for users who
already know their Brewfile is installed and don't want to incur the overhead
of brew bundle check.

[carlocab]

CC @Homebrew/maintainers, @jacobbednarz, @colindean for thoughts on this vs #19636

[MikeMcQuaid]

CC @Homebrew/maintainers, @jacobbednarz, @colindean for thoughts on this vs #19636

@carlocab and I chatted privately about the performance differences and, given that #19636 is a fairly major performance regression: I'm 👍🏻 on this approach.

Thanks for opening PRs to compare both, though ❤️

[MikeMcQuaid]

Thanks for making this easier to review! Would be great to have some more test coverage here but otherwise 🎉 ✅

[colindean]

LGTM on a visual check. I'd prefer the behavior here to that in #19636.

[github-actions]

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