templater: abstract ifcontains() over wrapped types This allows us to make .keytype private. There's a minor BC that a hybrid dict/list of keytype=None now strictly checks the type of the needle. For example, {ifcontains(rev, files)} no longer matches a file named "1" at the rev=1. I made this change for consistency with the get(dict, key) function. We can restore the old behavior by making keytype=bytes the default if desired.