[FIXED JENKINS-25234] Improve readability of the 'schedule build' tooltip

SCM._for is actually @CheckForNull.

[FIXED JENKINS-20606] Wrong spelling in Russian localization

Updating SingleFileSCM to nondeprecated overload of checkout.

This allows @Initializer to have parameter injection

This demonstrated that we actually need to call EnvVars.overrideAll explicitly (as CoreWrapperStep already did).

[FIXED JENKINS-19634] Fix sorting percentages