implements formula search fallback

This PR addresses #33635. The change: when `brew install` fails to find a formula, it now searches formula as well as taps.

Current behavior:

```sh
$ brew install racket
Error: No available formula for racket
Searching taps...
$ brew search racket
plt-racket
```

I found myself doing that sort of thing a lot. Now `brew install racket` does this:

```sh
$ brew install racket
Error: No available formula for racket
Searching taps...
Searching formulae...
plt-racket
```

I could not find documentation for the feature that searches taps after failure to install, which seems like the place to document this feature as well. The same goes for tests. However, in [my discussion](https://github.com/Homebrew/homebrew/issues/33635#issuecomment-60648380) with @mikemcquaid, he indicated tests and documentation might not be necessary for this feature.