This modifies cask-related livecheck strategies to allow passing a
regex into a `strategy` block, when appropriate. These strategies
were outliers that explicitly rejected a regex even if a `strategy`
block was used, forcing any regex to be inlined in the `strategy`
block (instead of being defined using `#regex`).

With these changes, all `strategy` blocks will be able to accept a
regex, further simplifying the mental model. This also helps to
better align the various `find_versions` and `versions_from_*`
methods across strategies.