livecheck: split cask versions into sub-versions

[SeekingMeaning]

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Follow-up to #10348

Livecheck now correctly reports 15.0.1,9 as newer than 15,36, but now 15.0.1,9.1 is reported as equal to 15.0.1,9

This PR adds the LivecheckVersion class that compares the individual sub-versions of a formula/cask version, similar to how the Version class compares version tokens.

When comparing 15.0.1,9 and 15,36:

1. 15.0.1 > 15
2. Therefore, 15.0.1,9 > 15,36

When comparing 15.0.1,9.1 and 15.0.1,9:

1. 15.0.1 == 15.0.1
2. 9.1 > 9
3. Therefore, 15.0.1,9.1 > 15.0.1,9

Related: Homebrew/homebrew-cask#98130

[BrewTestBot]

Review period will end on 2021-01-21 at 17:31:33 UTC.

[BrewTestBot]

Review period ended.

[MikeMcQuaid]

Not blocking but if there's a chance for tests for any of this that might be nice?

[vitorgalvao]

We’re considering getting rid of : in version. Pointing that out so there’s something to link to from the other issue, and we can revisit this code when the time comes.

[MikeMcQuaid]

Suggested change

	class LivecheckVersion
	class Version

or rename the file livecheck_version.rb maybe?