Recursively expand requirements in FormulaInstaller

Currently FormulaInstaller "forgets" about the requirements of
dependencies, as dependencies are recursively expanded by the first
FormulaInstaller instance, and then ignored by subsequent instances to
prevent duplicate installation attempts. These requirements then have
their messages displayed, but the fatal check is skipped and thus no
exception is raised.

Now that we have Formula#recursive_requirements, we can mirror what we
are doing with dependencies and recursively expand requirements up
front.

While at it, fix a bug in determining Requirement equality that resulted
in unique requirements being eliminated from a formula's set of
recursive requirements.

Fixes Homebrew/homebrew#12290.
Fixes Homebrew/homebrew#14084.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>