Update the used MediaWiki rule set to 0.12.0

[thiemowmde]

I reviewed the new sniffs that come with this update and believe they are all fine. But feel free to disagree, and briefly explain your reasoning. Better disable one or two disputed sniffs than not updating, because all these updates also come with bugfixes.

• LeadingZeroInFloat is not terribly important, but I think 0.1 is better readably than .1 and worth a sniff.
• ClassMatchesFilename is obvious, I hope.
• The new OneClassPerFile sniff does have a confusing name. It checks for classes, interfaces, and traits in one step and does not only replace the three individual sniffs, it does more that these: the individual sniffs are not able to detect cases with, for example, an interface and a class in one file.
• OpeningKeywordBrace just got renamed.

Warning, this is a chain of patches! #16, #17, and #18 should be merged first!

[manicki]

The new OneClassPerFile sniff does have a confusing name. It checks for classes, interfaces, and traits in one step and does not only replace the three individual sniffs, it does more that these: the individual sniffs are not able to detect cases with, for example, an interface and a class in one file.

The name is not the most accurate, but I actually think it is OK like this.
From the commit message https://phabricator.wikimedia.org/rMCSN0da3ec7107c84909c1217dffa2300ccb6f580803

The separate three upstream sniffs would still have allowed a class and an interface to be in a file together, which still violates PSR-4.

[manicki]

Also MW CS 0.12 dropped the Goat Sniffer integration, so I am not 100% glad of this change, but what better alternative do we have?

[lucaswerkmeister]

Well, removing more goats from more places would certainly be a better alternative, but if there are no more goats in the sniffers I guess this will have to do.

[thiemowmde]

All previous "one per file" sniffs have been replaced with Generic.Files.OneObjectStructurePerFile via #24.