This reverts commit e143bcef259ca76b2124e6e73bd9bdf872418723.

Closes Homebrew/homebrew#31557.
Closes Homebrew/homebrew#31559.
Closes Homebrew/homebrew#31561.
Closes Homebrew/homebrew#31562.

This reverts commit 4d1464c246861f7aedc355cb5f6360370d05114e.

This reverts commit 1c05bc0238aa1abf7d5542b8afa11ead2bee66a8.

This reverts commit cee42c339e7632eab15111e2c4e6c121ace6f9e2.

This reverts commit 8d2ef974a3a87bf4207f71ccb8a7b4776e16a016.

This reverts commit 6f29c36aed9d951499146054a4caca702fa33d1a.

See 5cd6b35 and 8eefd4e.

build.without? seemingly always returns true for requirements that are
neither recommended nor optional so check these before deciding not to
install a default formula.

Closes Homebrew/homebrew#31511.

Use the build options instead of whether the requirement is optional to
work out if it is needed. This handles the case of an optional
requirement becoming needed because it's a dependency for another
formula.

Closes Homebrew/homebrew#31476.

Now we can use the superclass options method for our own purposes.

We only need to process the legacy options at load time, not each time
the class is instantiated, and only when there is an options method
defined.

This reverts commit 435092ae0521e79d8ea21c8d4708031e3b4b17a3.

(Commit message written by Mike McQuaid)

With the change in a0a93f1b3b7b2be9b8a319be91086ffe220f8e32
unfortunately requirements with default formulae no longer could be
resolved when the default formulae were not installed. This commit
fixes this problem.

Closes Homebrew/homebrew#31476.
Closes Homebrew/homebrew#31444.
Closes Homebrew/homebrew#30901.
Closes Homebrew/homebrew#31471.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>