Xorg: Use PageMatch#find_versions

[samford]

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I'm working on extracting changes in #9535 that aren't specifically related to the migration from open-uri to curl into separate, topical PRs. This will help to minimize the number of changes in that PR, which certainly won't hurt when it comes to troubleshooting the hang we're seeing when using curl.

This PR modifies PageMatch#find_versions to accept an optional provided_content parameter, which allows the method to work with cached page content. When page content is provided, we don't fetch the content at the url (using Strategy#page_content).

Since the Xorg strategy tends to check the same x.org pages over and over for related formulae, we implemented a simple caching system to minimize the number of times we fetch these pages. As a result, Xorg#find_versions duplicates some of the logic found in PageMatch, simply to be able to work with cached page content. The previously-mentioned change to PageMatch allows us to modify Xorg#find_versions to simply use PageMatch#find_versions internally, like many other strategies.

Outside of bringing Xorg more in line with the other strategies, allowing PageMatch#find_versions to work with a content string is a first step towards enabling page caching throughout livecheck.

[BrewTestBot]

Review period will end on 2020-12-24 at 14:32:47 UTC.

[maxim-belkin]

👍🏻 Looks good!

[BrewTestBot]

Review period ended.