hevea 2.18

Also: add test, fix prefix.
hevea: add 2.18 bottle.

Closes #32434.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
hevea: reported inreplace upstream.
brew: add contributed tap commands to PATH.

This means that taps root and `cmd` directories are added to the PATH.

This should enable migration of some of our contributed commands into
taps (e.g. `homebrew-boneyard`) and make it easy for third parties to
be able to maintain these. It might also make stuff easier for existing
tools like e.g. `brew-cask` and `boxen`.
hevea: update 2.18 bottle.