generate ids for xxxHistory objects

[cropredyHelix]

use case:

Mocking xxxHistorySelector result records (e.g. AccountHistory, CaseHistory, customObj__History)

fflib_IdGenerator.generate(AccountHistory.SObjectType);

current behavior: null pointer exception PR: returns 017xxxxxxxxxxxxxxx

Notes:

OpportunityHistory returns `008xxxxxxxxxxxxxxx` (as this object has a keyPrefix available from Describe)
OpportunityFieldHistory returns `017xxxxxxxxxxxxx`
All other xxxHistory returns `017xxxxxxxxxxxxx`

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This change is