dev-cmd/pr-publish: fix undefined method error on invalid input

Audit: allow make check for nettle

docs/Formula-Cookbook.md: mention the use of 'bottle :unneeded'

shims/mac/super/xcrun: unset rather than emptying DEVELOPER_DIR

Co-Authored-By: Mike McQuaid <mike@mikemcquaid.com>

formula: make CMake SDK root choice consistent with superenv (+ SDK root refactoring)

Library/Homebrew/rubocops/uses_from_macos: add ssh-copy-id

bump-formula-pr: use Homebrew::EnvConfig

audit: Check if `uses_from_macos` usage is correct

Set HOMEBREW_GITHUB_API_TOKEN from GITHUB_TOKEN.

Remove old pkgconfig files.

os/mac/pkgconfig: supply default homebrew_sdkroot

If `HOMEBREW_GITHUB_API_TOKEN` is not set and `GITHUB_TOKEN` is: let's
use it. `GITHUB_TOKEN` is a somewhat standard env var to set for
GitHub authentication tokens (e.g. used by `hub`).

Homebrew::EnvConfig: unify environment variables.

Homebrew no longer runs on these macOS versions.

cli/parser but for environment variables. This makes it easier to set,
check, document and set defaults for environment variables in a single
location that can be used for query and documentation generation.

Add `mdimporter` stanza to homebrew cask DSL

- This builds on @jonchang's work that started in #6265.
- We now use `uses_from_macos` to declare dependencies that are implicit
  on macOS because they ship with macOS, but they're needed on Linux. We
  have to be sure that the dependencies people specify as
  `uses_from_macos` are actually shipped with macOS. So, we maintain a
  safelist of those dependencies and check against it.
- Also add more legitimate `uses_from_macos` dependencies to the list.
- This is runnable with `brew audit --only-cops=FormulaAudit/UsesFromMacos`.
- It produces different number of failures on macOS vs. Linux, because
  apparently we've not synced Homebrew/linuxbrew-core upstream thoroughly
  enough yet.
- Originally this was designed as a `--strict` audit, but we flipped it
  to be a normal audit because - to quote Mike - this is "sufficiently
  robust" now.

download_strategy: unlink the lock file after unlocking it

shims/mac/super/pkg-config: fix macOS <=10.13 compatibility