ICS28: Set initH in onChanOpenConfirm

[mpoke]

Currently, the initH mapping (i.e., it stores for every consumer chain the height when the first VSC was provided to that consumer chain) is set in the EndBlock after checking whether it was previously set. Since this is inefficient (i.e., lots of lookups), it is better to set it in onChanOpenConfirm once the CCV channel is established. Note that even if initH would contain a height h1 preceding the height h2 when the first VSC was provided, the validator set and the delegations between h1 and h2 will remain unchanged; otherwise, a VSC would have been provided.